The problem is they had a lot of guys making max money that don't make sense if there isn't that final superduper star on the team keeping everybody in line. Horford makes sense at big money because he's not supposed to be a main cog in Philly. In Boston he was the lone star big and he wasn't the type of leader that could control Kyrie. The Celtics often talk about how what Garnett brought to the team wasn't just his on court play, but his leadership. As the unquestioned alpha, he set the tone with his work ethic, competitiveness, and determination. Obviously, this is the opposite of what happened in the locker room last season.
In retrospect we had three max guys who were better off as the 2-4th options of a great team. In addition, Kyrie had a foot out the door, Hayward was recovering from devastating injury, and Horford was always just supposed to be the ultimate glue guy. He just isn't a vocal leader and his game and personality seem very deferential.
Now, in the absence of this kind of player leader, you might think Stevens was supposed to provide that from the coach's position. To this I'd probably say yes and no. Players often say that coaches can only do so much when compared to a strong veteran leader who is keeping people accountable. If Stevens says you better not go out late in Miami when we have a back to back, it isn't as effective a message as when it's coming from a vet star you respect.
I can understand all the moves, they were all justifiable at the time. But from a large picture view, it clearly didn't work from a title-chasing perspective. Davis clearly was the big fish they were hoping for, but if somebody doesn't want to play for you, there's not much you can do. However, as talented as Davis is, the guy is not mature enough to be a leader either. If he had come over and Kyrie had stayed, regardless of the overall talent I'm sure the team would have still disappointed.