The arc is filled with so many juggernauts that it's easy to forget how strong these flying six level characters are. You guys remember Pedro? The dude who was arguably stronger than 90% of the strawhat crew? He was an absolute fodder to Perospero.
Mans are so surprised the flying six are noted as strong that they've gifted them a level above veterans. Feel that's because people have been underestimating what it means to be a "veteran" level character to begin with, and underestimating the flying six because of that.
Tamago and Pekoms couldn't lick the soles under the veterans feet, and Tamago was stronger than Pedro. There are levels to the Yonkou crew, and some of the characters right below the calamities/commanders are monsters in their own right. Let's not even talk about the calamities, even someone like Jinbei doesn't hold a candle to characters on that level.
Realistically only Luffy, Zoro, Jinbei, Sanji (wildcard = Nami with Zeus) can deal with the flying six, but since this is a major growth arc where everyone is fighting someone vastly above their level, the others strawhats can chime in. Don't expect Zoro to be anywhere near King, nor is Luffy anywhere near Kaidou, so it's only fair the other strawhats get their equivalents of those battles.
Don't think people quite grasp how deep a Yonkou crew is, there are layers upon layers of strength in there, you didn't have Marines mobilizing everyone and their mothers for no reason, to deal with 1 crew and allies. A bit understandable since WCI made the BMP look like a circus act, but let's not get it twisted, there is plenty of room for heavy hitters below a level high enough to compete with and potentially overpower G4 pre adv haki (which the commanders have shown).