All this discussion about playable characters has me wishing for a new 2D spin-off series, handheld or not. While the 3D main series games have always struggled to implement extra playable characters, I rarely see any complaints on how the Advance and Rush series handled them.
Amy's gameplay in Advance 1 is considered superior to how it was in Adventure 1 and indeed it's one of the most fun gameplay when you learn how to use it. The worst I hear about Cream's gameplay in Advance 2 is how OP it is against bosses, which is easily rectified by simply not using the attack button. If anything, Cream gets hate solely for her archetype and usage in stories but her gameplay has never been a problem. And though I think a large portion of Blaze's appeal comes from her personality/character development, the fact that her gameplay is mostly the same as Sonic's with minor differences in both Rush games kept her from earning immense vitriol like the characters introduced in the 3D games did (i.e. Big and Silver).
If I have to wait for Sonic Team to get their shit together before characters should be allowed to become playable in a 3D main series game again, fine. But the waiting would be SO much easier if we could at least play as the other characters in SOME capacity outside of just the Mobile and Olympic games! Extra playable characters have never been a problem in both Advance and Rush so why not give us another one of those games so we fans of the other characters can be satisfied?