Finally skimmed/caught up.
Just saying, remember we are reading spoilers from like 3 panels. I'm not insinuating Kaido's son is stronger than Ace but realize the "competition" the F6 are having are just forcing Kaido's son to show up at a Party, not beat his ass into oblivion so they can challenge the All-Stars.
We have no idea what his ranking is if he has one. We still have no idea whether or not an "Ace" actually exists in Kaido's crew. It just goes back the state of the discussion we were having before 2 chapters ago when Kaido mentioned his son. If the Ace exists, he is either the Number "1", Kaido himself, or an unrevealed member of his crew. Its very unlike Oda to leave out the usually highest card value from a group of pirates named after card values lol.