I'm a Schumacher fan and I agree with you. I think his reasons for coming back were good, to help Mercedes develop and become a top team, but it seems the fighting spirit that made him what he is, just isn't there anymore.
Couple that with a car that hasn't really been great, and he looks average.
So on one hand he should have stayed in retirement, but on the other hand I don't think he ever believed he'd come back and win another title, but did it for Mercedes/Ross Brawn