Don't say pets with no damage are useless unless you state its your own opinion-

For everyone it's different. I've seen so many people whose alts are strong enough to cause all the damage required so their pets all assist/ seal: Shasha, eva, qlaya, xaolan, shizune etc etc etc even elin just for her high con to stay alive. Why? Because that's what their useful for within that team. If the alts were to lack in terms of damage as they were dominantly a sealing team THEN pets that cause decent damage would be useful.
Only other situation I can think of is those people that spend so much on the game to scroll their pets so they do a crazy amount of damage with a high amount of con so all the alts need to do is hf them. I don't see much benefit in this option other than saving a few rounds in battle.