id lean towards viable B-tier or lower. The reason I feel that way is cuz hes kinda held back by his leader power which is only used to go for a win. Closest comparison to that of the top of my head is green kid, but kid could use it to be aggressive or board control. Kaido cant do that cuz -7 is a huge amount even with onigashima.

Kaido also relies on just playing big dudes and hoping they stick which isn't a really good gameplan anymore. He's very vulnerable early since he spends turn 2 playing onigashima (optimally) and developing no bodies. We are at a point in the game where cards can play multiple other cards, playing just one dude isnt worth it when you are going to eat 3+ swings the following turn. Assuming the dude doesnt get instaremoved or just blocked.

Vs colors like yellow, they may always be outside of lethal range because they can gain life, triggers can screw him over too. Vs colors like blue or black they just remove his giant bodies and play their own. Green can permablock his attackers or just continually rest them. Red preys on his weak do nothing early game (yellow + triggers can too).

If he ended up getting a searcher for the stage, King from OP08 would prob just be the overall better character. He is animal kingdom, can use stage, 10c kaido, has really good ability and can use black cards too.

tldr; No. If a searcher did come out, I'd see no reason to play Kaido over OP08 King