it's definitely a problem sir, if we do it now. It's a domino effect.
Take Marvin away, and a guy like Zaza may have to play 5 - 10 more minutes a night, even if Horford assumes the backup PF role. Either that, or Shel / Solo have to get minutes. If you add a good quality center, then you're right. It's not a problem.
Add Miller to the squad, and we're deeper at the 2 & 3, which may allow JJ to rest more.
The best of both worlds would be to move Chill for Miller. The 9+ million a year deal probably kills that move though.