^Okay scratch the last part. Sorry I misread some parts. You're right but that's because the AI just sucks. Isabelle and Khalis main strength comes from their ult. You can't deny that as long as Isabelle casts her ult, you're guaranteed to die even if you have the elemental advantage.

Also this is just in Arena/ToT. In dungeon/raid I'd rather have Isabelle/Khalis as teammates because they're unmatched in dealing damage.