Talent is needed of course, but I think chemistry is the real differentiator. Looking back:
2023 Denver great chemistry
2022, 2015, 2017, 2018 GSW elite chemistry for all along with just pure elite talent for 2 of them
2021 Bucks very complementary players all having solid and accepted roles
2020 and 2015 Lebron LAL and Cavs teams are the 2 main exceptions here IMO, while his 2 Heat title teams I thought had very good chemistry
2019 Raptors had good chemistry, but a lucky season with GSW's injuries
2003, 2005, 2007, 2014 Spurs all elite chemistry of course
2011 Mavs great chemistry
2009 and 2010 Lakers pretty mediocre chemistry, but they worked well together
2008 Celtics had great chemistry
2006 Heat had well defined roles and role players
2004 Pistons great chemistry and identity
And that covers every NBA champion over the past 20 seasons. And the word chemistry starts to look weird when you type it so many times.
I'll be curious how the Celtics chemistry comes into form this season.
This is also the part that concerns me about Porzingis. After Tatum, the next three players Jaylen, Porzingis and Brogdon are all individualistic and not team orientated in their style of play. It is hard to have high caliber chemistry when your top guys are looking out for themselves more than the team.
I am not sure this is a true conclusion. Brogdon came the the Celtics and accepted a 6th man role, embraced the role enough to win 6MOY award. He did pretty much everything the Celtics asked him to do. And I don't know where you are getting that about Brown. We have been hearing for years that Tatum and Brown can't play together yet the team has done well and both players have improved every year.
On Porzingis, I think the farthest you can go is TBD. So far, Porzingis has said all the right things. The trade would not have happened if he didn't want to be here, he could have not picked up his option and not agreed to extend on fairly team friendly terms. That would have killed the trade and he would be a UFA right now.
I am not worried about "chemistry". Chemistry always appears good when teams do well. I agree that it can be a factor to some extent, but I am not sure what comes first; does good chemistry lead to winning or does winning lead to good chemistry?
If anything, Brogdon may be a little put off as a result of almost being traded, and the whole world knowing that. But I actually think he will deal with that just fine. He has been nothing but a consummate professional on the Celtics and his entire career. And if he does have some lingering issue with this, and wants out, he is easy enough to trade. I think all the players you mention, Brown, Brogdon, and Porzingis are very happy to be on the Celtics and all of them will do whatever is asked.
I would say that 90% of what is called chemistry is skill-based and is about having players (1) with team based skills [team offense, team defense, rebounding) and (2) who complement each other's skill-sets.
So when I say individual based in this context, I am talking about the style of play of Jaylen Brown, Porzingis and Brogdon.
Brogdon is more of a one-on-one type guard. He has nice floor spacing skills as a team offensive player but impact as a go-to option is one-on-one based. His playmaking and passing comes from one-on-one play. His driving ability. He is not a true PG in terms of being a floor general and setting up the team. He is a passer out of one-on-one opportunities. So he is either a one-on-one player who can be a 20ppg 6-7apg threat or a role player guy who is a 12-14ppg 3-4apg threat depending on whether he gets enough one-on-one opportunities. And ever since he blew up in Indy, he calls his number quite a bit. He looks after himself.
This isn't character based. This skill based. So yeah, Brogdon accepted a smaller role and came off the bench but he maintained the style of play he had in Indy just did in shorter minutes.
Jaylen Brown's issue is similar to Porzingis in terms of possessions used for scoring attempts (FGAs, FTAs, TOs) relative to possessions used to create an opportunity for a teammate (ASTs). Both are high volume scorers with low volume passing. This makes it harder to have good ball movement and team based offense. It makes the offense more likely to devolve into iso ball or my turn / your turn type offense.
This has been an issue for Boston for several years now due to Tatum and Jaylen. Tatum has gotten better in the last few years at this and is less of an issue now although he is merely good rather than great in terms of his balance of creating for himself vs creating for others. Jaylen continues to be an issue. Porzingis has been issue his entire career in this regard as well. So adding Porzingis is likely to increase this issue for Boston.
So the individual focus vs team focus I am talking about here is skill-based and style of play based. And this is why I consider each of these three players to be individualistic in their approach to basketball as opposed to team based.
With Jokic being the ultimate team based approach. Magic, Bird. The holy grail of team based style of play. Those three dudes. Pau Gasol team based. Kevin Garnett team based. Rondo team based. Pierce and Ray were more like Tatum level team based.
The opposite extreme would be guys like Rudy Gay or Corey Maggette. Some big guys like Al Jefferson. Or even our own beloved Kevin McHale who was a black hole in the post. Did not like passing out of the post. Hakeem Olajuwon was a black hole in the early years of his career before becoming more team based in the 90s when he learned the value of drawing double teams, passing out and creating easier opportunities for his teammates. Or Moses Malone. Some of these guys can go on to have great careers but they are a challenge to team offense and if you put too many of them on a team together they can limit your offensive ceiling due to lack of ball movement.
Sticking with McHale, just look at Boston's offense that year that Bird was out for the season and they tried to run the offense through McHale and Parish. Neither guy was a good enough passer. The offense kept stalling. Both were individual based on offense although team based on defense & rebounding so they were not as individualistic as our current trio (Jaylen, Porzingis, Brogdon) but they certainly were on the offensive side of the floor. You take Bird away and their flaws / limitations showed up much more clearly.