Honestly, seeing how many of them can easily bypass Kaido's dragon scales, it's even more impressive that Akainu remained unscratched even after encountering several Ryou users.
Marco AND Vista tried attacking him simultaneously - he just shapeshifted around their attacks only saying "Haki users, huh? Annoying!".
There are confirmed Ryuo users like Izo, capable of hurting Kaido, incapable to hit Akainu ONCE.
People often try to downplay Katakuri but see how useful CoO and shapeshifting really is. You guys think these Scabbards would hit Katakuri even once?
Stop underestimating FS and other attributes, attack power may be useful against tanks such as Kaido but match-up circumstances still matter. The Admirals are highly versatile in literally everything - top tier level CoO AND CoA + top tier DFs.