look, zaul is still viable and can actually give you some stuff. but if you are on a newer shard, i wouldnt zeta maul.
if you do have zeta maul, fine, you can use and have the inital TM and stuff like that. even team of Zaul+nest when you "force" the other team to attack nest frequently can work great... but if you dont have zeta maul, save the zeta, its not valuable as it used to be, and you can have cheaper temporary solutions in arena until you zeta the next upcoming meta (which we dont know who)
so i wouldnt zeta him personally, just save the 20 mats.