NBA Confidential: Why does everyone doubt the Boston Celtics?

The Boston Celtics had far and away the best record in the NBA this season. They also have far and away the best winning percentage in the playoffs (12-2, .857) making short work of all three teams they faced. 

Their collective playoff experience dwarfs that of the Dallas Mavericks, the last team standing between them and a coveted 18th championship, which would break their tie with the Los Angeles Lakers for most by a franchise in league history.

Because of all that, the oddsmakers have them favored to beat the Mavs when the best-of-seven Finals begin Thursday.

So why is there a healthy amount of doubt that the Celtics will actually make good on all that and be crowned champions sometime in the next two weeks?

That was the question posed to a collection of GMs, scouts and executives by FOX Sports. One Western Conference GM captured the majority perspective: "Boston is definitely the favorite," he said. "But I would bet on Dallas."

Responses included an array of reasons given for all the doubts about this Boston team. 

One is the Celtics' recent history. They've been here before, more than once, and failed to finish the job in startling fashion. Two years ago, they rode into the 2022 finals as the heavy favorite against the Golden State Warriors and took a 2-1 series lead before losing three in a row by double digits, the last one on their home floor. Last season, the collapse came in the Eastern Conference finals, when they pushed their series with the seventh-seeded Miami Heat to a seventh game, only to get trounced — again in the friendly confines of Boston's TD Garden, one of three home losses in the series.

While the Celtics made several major additions last summer — dealing the gritty but erratic Marcus Smart for a steadier hand in Jrue Holiday and upgrading from the oft-injured and offensively limited Robert Williams to one of the best stretch power forwards in the league, Kristaps Porzingis — there are still questions about the team's two main stars, Jayson Tatum and Jaylen Brown, being able to deliver in the clutch.

"They are good," said a Western Conference executive, "but they still need to get the monkey off their back."

The monkey remains even though Tatum and Brown have not had any of the dud performances this postseason that created those questions. If their recent showing has been discounted, it's because of who the Celtics have faced — teams missing key players, including stars who might have raised the bar for Tatum and Brown in crunch time. 

The Miami Heat were without Jimmy Butler and Terry Rozier the entire series. Their second-round opponent, the Cleveland Cavaliers, were without starting center Jarrett Allen (rib injury) and then leading scorer Donovan Mitchell bowed out with an ankle injury after Game 3. Their conference finals' foe, the Indiana Pacers, lost All-Star point guard Tyrese Haliburton to a strained hamstring in Game 2.

Then there is their opponent, the Mavericks, who have the golden sheen of the team no one saw coming. If the Celtics are viewed as perennial favorites who fall short, this year's Mavs have the aura of a team that has repeatedly defied its underdog status by playing its best in the biggest moments. The Mavs upset the LA Clippers in their first-round series, stealing the homecourt advantage by winning Game 2 in Los Angeles and wrapping up the series in six games. Exactly how good Dallas was remained unclear, because the Clippers were without Kawhi Leonard (knee inflammation) for the last four games. The Mavs rolled into the next round as even bigger underdogs, facing the west's No. 1 seed, the Oklahoma City Thunder, and promptly got smashed in Game 1 by 22 points. But every time they needed a virtuoso performance — and a win — they got it, culminating with a 117-116 win in Game 7, in Oklahoma City, after trailing by as many as 17 in the second half.

It appeared as if the Mavs not only responded to having their backs against the wall, but that it was their happy place. Surely, though, Anthony Edwards and the Minnesota Timberwolves' top-ranked defense, fresh off of taking down the defending champion Denver Nuggets, would change that. After all, hadn't the Timberwolves beaten the Mavericks three out of four times in the regular season? None of that mattered. Luka Doncic and Kyrie Irving promptly roasted the league's No. 1 defense, orchestrating an offense that shot 50% and flipped the Timberwolves' regular-season net rating of plus-6.6 to minus-6.3 for the series.

"Dallas is either the best team in basketball or on an epic heater," a second Western Conference GM said.

The Mavericks defying what their regular-season results say they are is one reason Boston's statistical superiority isn't carrying a lot of weight. Another is who they compiled those numbers against. Most of the survey respondents considered the Celtics' league-leading wins (64), margin of victory (11.4) and net rating (11.6) the product of being, at least in part, in the weaker Eastern Conference. The Celtics were one of two 50-win teams in the East — New York was the other — while the Mavericks were one of five in the west. The East also had eight teams with winning records, while the West had 10. And the two worst teams in the league were both in the East, the 14-win Detroit Pistons and 15-win Washington Wizards, both seven games behind the West's two bottom dwellers, the Portland Trail Blazers and San Antonio Spurs.

"If Boston had been in the West, their record would have matched the West's top four," the Western Conference executive said. "Five teams in the East were tanking and two more were under .500. The East schedule was so much easier."

The Celtics' 3-5 record against the top four teams in the west — Oklahoma City, Denver, Minnesota and the Clippers — does suggest their superior overall record didn't reflect a clear superiority over the west's best.

"Boston hasn't played any decent teams in the playoffs and had the easiest regular-season schedule, so it's literally impossible to tell if they are the best team in basketball or would have been eighth in the West," the second Western Conference GM said.

Anyone rooting for the Celtics, of course, is quick to point out that their team isn't facing any of the top four teams, but are up against a Dallas team they beat decisively in their two previous meetings, both before the trade deadline moves that transformed the Mavericks into what they are now and well afterward with a 138-110 beatdown in early March.

The Mavericks, though, are notably different even since that last meeting. Rookie Dereck Lively II started that game, along with Josh Green. Tim Hardaway Jr. and Dante Exum were mainstays in the rotation. Derrick Jones Jr. played seven minutes, scoring one point. Jones is now the starting small forward and has emerged in these playoffs as a classic 3-and-D wing, shooting nearly 40% from beyond the arc while averaging nearly two blocks and six rebounds a game. Lively is coming off the bench behind a more experienced Daniel Gafford. Green and Jaden Hardy have replaced Exum and Hardaway Jr. in the rotation.

"I'm not sure Boston faced this version of Dallas in the regular season," a second Western Conference scout said.

Mavericks coach Jason Kidd is credited with not only re-working the rotation but convincing his two stars, Doncic and Irving, to find a balance between taking over with their individual brilliance and feeding their teammates on offense. As good as Tatum and Brown have been this postseason, the league consensus is that the Mavs have the top two playmakers in the series — and the best sideline decision-maker, with Celtics head coach Joe Mazzulla's hands-off approach drawing criticism despite all of Boston's success since he took over last year.

"I still don't trust Mazulla, I think he is their weak link," a third Western Conference scout said. "He's gotten better, but he has no seasoning, going from back of the bench to head coach. And Tatum is going to have to do it when it is all on the line, which he hasn't done yet. They are so talented they could've got this far with (Joe) Biden coaching them. Their only test is going to be in the Finals."

Kidd's rotation changes were made to bolster the defense around Doncic and Irving, but it also appears to have inspired those two to raise their effort as well. One Eastern Conference scout credited that to the rim-protecting duo of Gafford and Lively, assuring that Dallas almost always has a rim protector on the floor.

"Everyone talks about the trades helping the Dallas defense, which is true," he said, "but what is not added is that Kyrie and Luka can get into the ball handler more knowing they have rim protection behind them."

The Celtics' rim protection comes primarily from one player — Porzingis — who has been out of action for more than a month now since injuring his calf in Game 4 against the Heat. How vital is he? If he were healthy, several survey respondents said, it would shift their view on the series. But his availability for the finals remains unknown; and even if he plays, the question is how much impact the month off will have on his overall effectiveness. Not having him has moved Al Horford into the starting lineup, reducing the strength of Boston's bench and tilting the advantage in that department, in most eyes, to the Mavs. The Celtics arguably have the most talented starting five, but "how many minutes can that great starting unit play?" asked a fourth Western Conference scout who picked Dallas to win the series.

"I believe Dallas is more balanced between offense and defense," a fifth Western Conference scout said. "Boston has an explosive offense when shooting well. They're excellent in fast break and transition offense and solid defensively. But they're not physical, they resort to ISO basketball when forced to play in the half court and without Porzingis they struggle to produce any inside scoring. There's the old saying: Live by the jumper, die by the jumper."

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There is a way in which the Celtics could look at what happened in 2022 as a harbinger in their favor, in that their path more closely resembles the one the Warriors took that year, and, conversely, the belief in the Mavericks is generated by a lot of the same factors that had the Celtics' 2022 bandwagon brimming. Boston began its 2022 run with a sweep of the Brooklyn Nets and their two stars, Kevin Durant and Kyrie Irving; they then knocked off the defending champion Milwaukee Bucks in a tough seven-game series, followed by another seven-game nail biter in which they bested the East's No. 1 seed, the Heat. All of that was supposed to make them more close-game ready than the Warriors, who had cruised past a parade of opponents missing their stars — the Nuggets without Jamal Murray or Michael Porter Jr., the Memphis Grizzlies without All-Star guard Ja Morant for half the series and the Mavericks with a hobbled Doncic.

Sound familiar?

In the end, of course, the more experienced Warriors came through. Could the Celtics do the same? The one survey respondent who has the Boston winning this year's title, a second Western Conference executive, believes they can.

"I don't have doubts or need to see anything from them," he said. "But it does feel like they're going to have to prove it before we all believe it."

Ric Bucher is an NBA writer for FOX Sports. He previously wrote for Bleacher Report, ESPN The Magazine and The Washington Post and has written two books, "Rebound," on NBA forward Brian Grant's battle with young onset Parkinson's, and "Yao: A Life In Two Worlds." He also has a daily podcast, "On The Ball with Ric Bucher." Follow him on Twitter @RicBucher.