Majority of Crab attacks are garbage. With the exception of Venom Grenade. Even Omega Maneuver is on a 6min cool down. You're better off taking huntsman attacks than Crab attacks, thats how bad they are.
Crab pets are also terrible if you're trying to solo, they die way too quick. They are good for melting hard targets like Pylons, but outside of that is subpar. Crabs I think really need a taunt aura and fill in a more tanky role, this way their pets and stay alive, the Crab's own subpar damage can somewhat be justified.