Yeah, Sakurai, as great as he is, can be a tad bit self-absorbed at times. However, that's not to say that it's always a bad thing. A little ego is good, since it apparently gives Sakurai a drive to make sure his games are the best they can be, even if it's not in his best interest. I guess it's ironic, in a way, since Sakurai's ego forces him to make sure that he's part of every facet of Smash 4's development, but at the same time, he's injuring himself. Anyway, it can be a good thing to have a little ego. If Sakurai thinks the series will go downhill if he leaves, then, as silly as that is, let him think it. If it drives him to make sure his games are great, then it's a good thing.
However, I agree that Kirby's and Kid Icarus's representation is too skewed and too much, respectively. I wouldn't mind if Sakurai's ego deflated just enough to not be as biased towards those series.