I think we all just vastly underestimated the Scabbards...all we’ve heard about the denizens of Wano, both from pirates and Marines, is that they’re all formidable swordsmen/warriors with capabilities well beyond most other fighters in the OP world, to the point where Akainu was somewhat hesitant to send Kizaru there. It’s been difficult to believe because Kin’emon/Kanjuro/Raizo were just dicking around for most of the time we’ve known them, but now that they’re all getting serious, we can see why everyone fears them.
Will they defeat Kaido by themselves?? The prevailing wisdom is that they won’t, but honestly, it wouldn’t be that surprising to me if they brought him down before Luffy and company can deliver the finishing blow. Gotta also consider the fact that the straw hat doesn’t necessarily have to be the one that beats the Yonko; Kaido’s defeat (and Big Mom’s) will open a huge vacuum in the world’s balance, and just like WCI, Luffy could end up getting credit just for being involved. The Scabbards won’t be looking for notoriety after Kaido goes down, so what’s to stop everyone outside of Onigashima from believing Luffy was that vital to the raid?
It would be a cop out narratively, but look - Luffy is currently strong enough to beat a YC1, which means he’s more powerful than anyone on the seas outside of the Emperors. Even if he doesn’t contribute that much to Kaido’s defeat, he’s still capable of holding his own (and winning) against any other challengers to the title he’s trying to gain. He doesn’t have to be the one to overcome the obstacle just to advance his quest; if it’s done for him, the end result is the same. The Scabbards have always had more motivation to put the hurt on Kaido than our protagonist, and we’re now seeing that they collectively have the strength to do so. Wouldn’t it be more poetic for them to avenge their master than have Luffy hog all the glory, even though he inevitably will?