Blue is simply a Carnival class.

It has no practical application outside of the Carnival. It's designed so that you get carried through levelling, get carried through dungeons, get carried through EX primals and then you're done. There is no reason at all to form Blu groups for content when you get no extra rewards, can't rez, have inferior dps, inferior tanking ability and one healing ability. It's not designed for playing outside the carnival.

Being a Carnival class has gimped it because it has to be balanced around the carnival. That's why it has tons of the same 130 potency element aoes and gimmicky status abilities, why mighty guard wrecks your damage and Diamondback isn't an immunity. That's why BLU doesn't feel OP.