What GhostTruckin said.
Royal Guard and Zeb are also possibilities for stun. Fett and Old ben for ability block.
As you level up he will become less of an annoyance. Phoenix Squad does wonders when he mass attacks and they all counter.
Anyway, as you level, and get a broader array of teams to work with, characters like that become easier to deal with. You just have to learn who and what works against each particular character or team AND have that counter available.
At your level, it was Darth Nihulus lead with Count Dooku that aggravated me. Stupid Count wouldn't die. If I saw that in arena, I just avoided it.