Phoenix has plenty of potential despite gimick. She has a decent life bar when you consider dark phoenix as he second half. so with lvl 5 it takes 2 combos to kill her not 1. Also you can tag out dark phoenix and her assists become buffed. Her assists as Dark Phoenix might be insane. Also, what if she tags out while in her healing bubble? If she can retain that as an effect on tag in she'll be insane on assist and her already powerful glass cannon point.
She has a TON of risk but her rewards seem on par. I can definitely see her being decent or broke
BTW...it seems as though this is the final roster for release but they ARE revealing more characters very soon, expected DLC. So no more leaked lists, all mystery here.