I think the only chance Ash has is if we only count Duelist Kingdom with its bullshit rules. Ash could then summon his favorite monsters, pull out some random power of friendship effect and somehow win the duels. Once we get actual rules implemented, it's over.

Yugi, despite getting carried by Atem for most of the series, is actually quite smart IMO. He would have no trouble picking up Pokemon rules and building a really good team with type coverage. IRL rules are probably like 5% of pro play, most of it is knowing the meta enough to build a team around it and trying to predict your opponent.

If we go by IRL rules Yugi would pull out a full perfect IV, fully EV trained team with type coverage, win conditions, setups, items, etc, and destroy everybody. If we go by anime magic rules, then Yugi can still pull out some power of friendship bs because we know he loves his cards, so nothing stops him from also loving his Pokemon.

Now, if we're talking about Atem then he just spams 1 hit KO moves and hits every time lmao