yeah..he is sort of squishy in arena with base stats. He takes damage with ninjutsu pretty decently although having a scaling defence. Lightning blitz, mabui-tenten teams c*most kill him in one round if he receives a combo. Thats why they run him with healers or leech in arena, even gakido or kurenai could help to survive first round onslaught. Once he is buffed up he is as good in arena as normal PvP.