I get that players and teams that have already won are perceived to be more likely to win again, but the teams with the core of their main pieces still in place that have won before are DEN, GSW, MIL, and LAL. The Lakers had a nice run last year, but I don't think they have the horses this year. The Warriors appear to be a .500 / play in team. They have work to do to get out of the play-in tournament. They've played better the last couple of weeks, but I still don't love their chances as a finalist. I suppose the Bucks have time to right the ship, but for now they don't look great. The Nuggets didn't win anything until they suddenly did. A team has to win their first title together before than can win a second.
The two other notable guys that have won titles before are on different teams now (KD and Kawhi). Harden / George / Westbrook / the Clippers haven't won before . . . does that matter?. Even if the Sixers get Embiid back, they haven't made it past the second round. The other young / limited experience teams (CLE / NYK / OKC / MIN) are unlikely to win 4 series, but they certainly could win a series or two.
As far as BOS goes, there has been a lot of talk that the C's won't win with Tatum as their main guy and point to their lack of a title so far. But he's still only 25. Durant won at 28. LeBron first won at 27. Jokic won at 27. Curry first won at 26. Giannis won at 26. Kawhi first won at 22 (but was not the main guy back then) and won as the top dog at 27.
At some point playoff experience should start to matter, right? Total playoff games for players under age 30 currently in the Top 30 in scoring:
Brown (105)
Tatum (94)
Giannis (79)
Jokic (68)
Embiid (53)
Mitchell (44), Booker (43)
Bridges (39), Brunson (36), Maxey (35)
Doncic (28), Young (27), Jackson Jr. (23)
KAT (16), Randle (15), SGA (13), Edwards (11)
Fox (7)
Markkanen, Banchero, Cunningham, Zion, Haliburtron (0)
Even though the Celtics haven't won a title, Brown and Tatum have a ton of playoff experience compared to many other younger players. IMO, that helps them a lot more than their lack of a title hurts them. I still say anything but a trip to the finals will be a massive disappointment for them.