You put all these stars together, and then the coach has to figure out how to make the team better. OKC is now in that situation, along with the Celtics and the Wolves. You know these teams can get better, but only at the sacrifice of individual stats (usage) of each of the stars.
For example, adding Melo to George and Westbrook is bound to drop the usage of each , and that will figure in fantasy drafts. Adding Butler to Wiggins and Towns will do the same to each. And then there's Irving, Hayward and Horford. I doubt you'll see monster stat years from any of those guys compared to last year.
Now this has no bearing on team performance--with the right coaching, these teams will be improved. But it will affect fantasy drafts.
GS is an interesting case: KD and Curry worked without losing much usage, but Green, the other major player, is not a scorer. Houston has added Paul to Harden, but two stars won't make as much a difference as three.
Putting three stars together should improve a team, but their individual stats might take a hit.