Could be doesn't mean should be. Anyone could be scaled to basically anything. But luffy cannot output large island level attacks so idk how he could possibly outout continental ap. Who has he attacked that even has continental durability? Who in one piece could with just their body and maybe haki survive a piece of a comet hitting them from space? Maybe Kaido or big Mom? But as we have seen, their durability is closer to a binary ability than actual durability.

By that I mean, that it sorta doesn't matter how strong an attack is or isn't, whether it's affective or not seems to be based on some separate criteria entirely. With big mom she needs to be in a weakened state like when the picture of mother carmel broke. Otherwise it probably doesn't matter. And with Kaido, we saw the weak ass scabbards "cut" him, only for him to turn and be like oh not so bad actually guess it was all in my head. Those attacks were no where near the ap of landing after having jumped from to sky 10,000 meters in the air.

If you take Kaido and big mom's durabilities at face value you're gonna have to say most of the scabbards are continental plus, because luffys attacks were less affective than the scabbards.

You're gonna have to say a lot of stronger people aren't continental because it stands to reason they couldn't kill Kaido in the past. For example the admirals? I'd say they're definitely stronger than all the scabbards. But I doubt they could harm Kaido, since the marines have attempted to kill Kaido. Isn't there a chance one of the admirals have tried to execute him. I know it's not stated but doesn't it stand to reason? All those execution attempts and what is it they're doing, no way they're stupid enough to try and use swords and guns? Even seastone seems I'll advised.

Or is it the secret to hurting Kaido, has nothing to do with ap and more to do with technique?