This team played a lot more like a team compared to last year for most of the season...I think the issue is that under pressure they revert to hero ball.
To me it is more a lack of skill.
Tatum and Jaylen are still young works in progress on offense who are far better at scoring the ball than distributing / playmaking with the ball.
So when your two go-to-guys are like that it puts pressure on other people. Those people tend to be (1) a playmaking PG (2) a facilitating big man (3) playmaking wings.
The loss of Horford robbed Boston from #2.
Kemba (#1) is more of a scoring PG than a playmaking one. He will give you some playmaking but largely through the threat of own individual scoring -- meaning the ball is being worked more through him and not Jaylen or Tatum (risk of peripheral than balanced).
#3 - Hayward was playing hurt and not his best self. He gave what he had but he couldn't do what was needed. I am not sure Kemba was really healthy either. Throughout the bubble Kemba wasn't attacking on offense the way he was earlier in the season.
Which forced more responsibility on Tatum and Jaylen to be playmakers / distributors --- which leads to more one-on-one hero basketball because they do not have the skill-set to provide teamwork based offense yet. They needed others to help them and that help wasn't available.
That is how I view the hero-ball in the playoffs. Injury to Hayward. Alright but not great performance from the scoring PG. No playmaking big men to help ball movement. Leading to Tatum and Jaylen being asked to do things they are not yet good at. And Smart being asked to do more than he is capable of too.
So more skill-related than mentality or coaching.
So much of today's offense is 25 feet from the basket. If you lack those playmaking skills and do not have enough team passing & playmaking elsewhere -- you end up with hero-ball type situations. You see that around the league. That is what I see here with this team.
We need more team passing. More incisive passing. The great thing about a passing big man is that the ball goes inside the three point line and moves out. In and out. Dribble penetrators create a similar unbalance to opponents defense with the drive and kick. The problem is without these you end up with more sideways passing around the three point line that does not take the opposition out of position on defense.
Celtics do not have a big man to run the offense through. With Hayward not fully healthy and Kemba being so-so (probably not healthy either), they lacked the dribble penetration also. Smart is limited by lack of quickness. Jaylen and Tatum by lack of passing. More self-creators than team creators. So you get hero-ball rather than team-offense.