Splitting up Mario's moveset and arbitrarily gating stars based on character simply isn't fun.
>just get a cap
Why is that fun though? Yoshi is interesting at least since he has a unique moveset and isn't "Mario but worse" or "Mario but better".
The effort spent towards the new characters would be better served making new levels like Block Fort, Sunshine Island, the Goomboss stage, etc.
We could've had courses within courses within courses but instead we have "please go back and pick Wario to break this black brick because fuck you"