Brad Stevens can turn that roster into a championship, particularly if Leonard and Butler head to LA, although it sounds more likely with Kyrie.
To my mind, Stevens's hallmark so far as an NBA head coach has been that the more talented his team is, the less successful it becomes (and vice versa). I'm not sure that adding another superstar to the roster at the expense of depth plays to his coaching strengths.
Although (and to some degree: of course), better players make a better team most of the time.
In the last decade, teams only win a championship with a top 5 guy:
2009: Kobe
2010: Kobe
2011: Dirk (probably around the fifth best back then)
2012: LeBron
2013: LeBron
2014: Kawhi
2015: Steph
2016: LeBron
2017: KD and Steph
2018: KD and Steph
2019: Kawhi
2020: AD in Boston? Do you really think it’s going to be 2020: Tatum?
Heck, I’d go so far as to say that 2019: Kawhi entry would be for Boston had we traded Brown and Rozier last year. We cannot make the same mistake. It’s absurd how this forum thinks Tatum and/or Brown will blossom into top five guys. Maybe top 10-20. They will almost surely never be as good as AD is today, particularly with AD as the fourth or fifth best player in the league after Kawhi, KD, Curry and LeBron.
You know what's absurd? Thinking 2020 is the end of the NBA. Barring an asteroid or some other cosmic malady, there will be a 2021 season.
You know what else is absurd? Chucking it all for a one year shot with a guy who's let it known he doesn't want to be here. I'd have thought Irving bailing on us would have been a lesson to those who want to go all in on AD.
Absolutely. I am sure the absurd Toronto Raptors agree with this.

Toronto gave less for a better player. Amd also got green in the deal.
I dont think its really comparable. I mean I wouldnt trade brown or tatum for demar. Spurs traded the best player in the world for him.
If Toronto lost in the second round the trade was still worth it because they dropped demars terrible contract.
They really didnt risk anything. They needed to move demar...this was an absolute steal of a deal for them.
That's a whole lot of Monday Morning Quarterbacking right there. At the time of the trade Kawhi had been out with injury a whole season. The reports were strong, and still are, that wherever he went other than LA, he would be gone in a year. So no one knew for sure how good or how much Kawhi would be able to play. San Antonio had to include a very good player to package with Kawhi because Kawhi's health was such a question mark.
At the time of the trade, and still today, DeRozan is a way better actual NBA player than anyone the Celtics will be trading for Davis. And Davis is 100% healthy.
The situations aren't exact, but extremely similar.
The Raptors and the Celtics would both be gambling on trying to win it all in one year to convince a top 5 player to remain on their team for more than a year. There is nothing false about that statement.
I dont believe anyone felt that kawhi was not healthy at the time of trade.
I dont believe that Demar us a better nba player than brown or tatum and certainly far from better than the both combined with smart.
And green last season wasnt a great player. He resurrected himself this year.
I belive the raptors had more talent left on their team than we would, at least better role players and depth than boston would after a deal for davis.
And Kawhi is and has been without a doubt the best player in the world. And the "injury" aside davis had an injury bug as well.
I firmly belive that the raptors had a much easier gamble to take and a much easier time to make it come true than the celtics would with Davis.
But there are similarities...i absolutely agree with that.
After the kawhi trade i had raptors as contending immediately. After the gasol trade there was no doubt.
I am not sure i would put boston in the top 5 of the league if they traded what is rumored for davis