The problem is that Greninja doesn't quite fit SM's roster and tone. Ash doesn't have Waterium Z (though he could use Normalium Z) and, unless they regressed him to his Froakie personality or something, Greninja doesn't really fit the comical laid back tone of this series. We have a team of quirky pets and then this giant super serious and stoic humanoid frog.
Plus people really want his Alola lot to get more battle time, adding an earlier powerhouse just exacerbates that.
Plus people really want his Alola lot to get more battle time, adding an earlier powerhouse just exacerbates that.