He's worse than most of Cosmic class, but not fully useless. I mean, he's better than Both Groots, Black Spidey, Superior Iron man and OG cap/miss Marvel, maybe he's on the same level as Kamala and Drax. I think all other Cosmics are better than him. If u have Cosmics other than mentioned AND IF U ENJOY PLAYING THEM MORE THAN BLACK BOLT (its the most important thing in the game), level up them instead.
However if you have Medusa and Karnak their royal synergy rocks.
He's basically a placeholder in a synergy team at the moment. He's poison immune with reliable stun and armour break; so you can make use of him; he's just a lot less helpful than most later Cosmic champions.If he gets Awakened (don't even think about using a Gem on him!) he can combine permanent Fury effects with Poison Immunity, which makes him useful against those rare opponents with Caustic Temper.