Heaven forbid people having different opinions, right?
Also, as someone who wanted Wolf in the game, there's no way in hell I'm going to discredit effort and new, unique characters added to the roster. Brawl didn't have Mewtwo and that didn't make it a bad game, which was still full of new and creative characters.
Even more ideal would be having all veterans back, because why the hell not? However, you can't have everything you want.
Corrin is a questionable choice, but I think Sakurai's point to add him was clear: he does offer something no one else in the roster does. Whether you agree or not is an opinion.
By themselves, character additions aren't good or bad. People just perceive them as good or bad, according to their own tastes. Likewise, Sakurai has his own opinions in which characters are added to the roster. If it were someone else doing the roster, things would have turned out differently, though neither better nor worse.
Radiant Dawn has multiple story parts. Ike is important later on, though Micaiah is focus for the first story arc.
Towards the end, both Micaiah and Ike are the central characters.