As already mentioned in this thread, Boba is a counter for Boba. Because if you execute Boba, he will not respawn. So if you are in such a fight, save your execute ability until enemy's Boba is in the yellow/red low hp area and finish him with execute.
I must say that I laugh about enemys that have Wedge, Biggs, Lando, STH and QGJ in arena. At least if the AI plays the team, GQJ is totally useless, no matter what gear he has, or even if these whales who are already lvl 80 play it against me with lvl 72.
He doesn't even remove the taunt and has such a low health pool that he is easily oneshot by Wiggs, whereas Boba cannot be oneshot. Well, actually he can but will respawn.
There are only two dangerous team comps for me (Wiggs Lando STH Boba) atm:
Chaze Jyn Wiggs
Copies of my team with better mods.