I disagree with the premise. Teams are built differently and should play to their strengths.
This Celtics team was built to have 5 main scorers - Kyrie, Hayward, Horford, Tatum and Jaylen. Kyrie and Hayward the two main scorers with the other 3 in supporting scorer modes.
Hayward has failed to fill that role due to his injury & recovery. That combined with the chemistry issues in the starting lineup has led to Morris and Smart having larger roles than expected.
Morris should have been a 20-24mpg backup. Instead Morris is playing 28mpg and dude is scorer. He touches it, it's going up. That is the way he is wired. Smart has done a great job of reducing his shot attempts this season to give others room they need to impact the game with his scoring.
Rozier should not be playing 23mpg and he should not be not taking 8.5 FGAs per game. There simply isn't enough court time / playing opportunities for Rozier to make full use of his talent. Kyrie is the lead guard. Then comes Smart. Then Boston has 3 wings in Tatum, Jaylen and Hayward. Plus some minutes for Morris at forward and some for Horford too in bigger lineups. There isn't enough minutes left over for Rozier to be a 20+mpg player on this team. It makes Boston too small in the backcourt and causes more problems than it fixes. Stevens needs to limit Rozier's court time and make him (or Wannamaker) a 10-12mpg player instead. If Rozier can control himself then he is obvious choice for that role. If he cannot, which he hasn't been able to do with any regularity or consistency this year and is likely to find it even more difficult to do so in an even smaller role, then Stevens needs to sit Rozier's ass on the bench.
That leaves Boston with 4 go-to scorers in Kyrie, Horford, Tatum and Jaylen. Smart and Hayward as supporting 7-8 FGAs role players. Preferably Morris in this role as well but he might get up there (10 FGAs per game if his minutes stay high) too due to Hayward's inability to break through this season (thus far).
I see Kyrie as a 15 FGAs a game type player. He can obviously do more individually but for the balance of the team I prefer to see him be more judicious in his shot attempts in order to create better team harmony. Keep others involved in offense so that they engage on defense. Then Horford, Tatum and Jaylen all in that 11-14 FGAs area (high low depending on who has it going on that night).
If Hayward had of been healthy, I view him as a 13-14 FGAs per game player. Again, he can do more but would need to be more judicious on this team due to the abundance of scorers. More of a 19-20ppg than a 22-24ppg scorer. With Tatum, Jaylen and Horford all taking a step back to a 10-12 FGAs players.
Tatum is the biggest issue in terms of the non-Kyrie scorers. He needs to stop trying to be the 2nd guy and be more of a team player. More like he was last year. His game isn't ready to shoulder that nightly load of being the #2 option. He is too reliant on medium efficiency shots and does not create at all for his teammates. It doesn't make sense for him to overdo it on a team with so much scoring support. Tatum needs to share the ball more and instead invest that extra energy in his defense & rebounding.