Umm no? Not utterly useless. The other option is he's just dead period. At least the passive gives him a chance at survival and then (if he doesn't die to damage debuffs, which isn't gonna happen 100% of the time) he can A3 to not die. The passive only happens if he was gonna die anyway, so I'm not sure what you're complaining about? I'm not quite sure you understand the Champion's mechanics and the fact that his passive gives you a CHANCE to survive... instead of just being dead anyway.
You do realize the point is that he doesn't die to a nuke in Arena right? Poisons are extremely rare in Arena, HP Burn isn't very common either... if there's Bombs then it's likely the bombs already went off and shifted him to his other form so they're not a threat now. The only legit thing you mention is Soul Reap and the exact same complaint can be made about Siegfrund if he has block buffs. Siegfrund still dies to Soul Reap if he can't put the Block Damage on himself AND he isn't guaranteed to go next, he has 100% Turn Meter Which again, if you're experienced in Arena, you'd know that Wukong gets 100% TM and he doesn't always immediately go after he revives BUT Nais is essentially guaranteed to go next...