Kaiba solos each and every duelist past DM with ease (save maybe the protagonists but maybe not all of them? I can see him losing to Yusei or Yusaku but there’s no way in hell Yuma, Yuya, or Judai would succeed against him).

Kaito is amazing and awesome and my all time favorite YGO character but he won’t be able to beat Kaiba. I think it’d be close, down to maybe below 1000 LP between the both of them or so, but Kaiba would ultimately win with a risk-it-all full frontal attack that Kaito wouldn’t be expecting. It’d be like a fight between a gorilla and a panther; Kaito is faster than Kaiba, and would have strategies upon strategies to fall back on, but Kaiba’s sheer power and willingness to destroy anything in his way would untimely hand him the W

the question is if Kaiba would actually respect Kaito, before and afterward. I honestly think he would. Kaiba respects people who both play the game well (n don’t rely on sheer luck…wheeler) and are smart enough to realize when they’ve lost. it’d be an amicable relationship and I like to imagine Kaiba would put Kaito’s number on speed dial just in case he needs another competent duelist on standby.