That's true .... but his solo career music is all Pop & while it appeals to the masses his best MUSIC definitely came out of his time with the Genesis. That's usually the way though, when everyone teams up to produce something special. YES is another band for example, where all the members produced solo efforts but when you put them together they sound so much better than their individual efforts.
No one person should ever be indispensible. It would be a travesty if just because Shigeru left that Nintendo were to fold. And that is a little disrespectful to everyone else employed by them. Now IF it came to pass that they collapsed ...well ... that's a different story ...