We have a different idea of useful, at 3 stars doesnt have time to get extra life or deal high damage with his jumps.
So at 3 and 5 stars it makes him bad at defence as I can blow him up before he does anything at all and for offence I have so many other heroes I can use that I do not need to rely on a 3 star rayman.
Dont get me wrong at 7 stars he is insane, if I had him at 7 stars I would use and gear him in a heartbeat butat 3 stars I find him massively underwhelming.