Do you get the feeling that King is underdeveloped/underutilised as a character? At least compared to his fellow Calamities?
Jack was the main antagonist of Zou.
Queen was a main/secondary antagonist in Udon and even on Onigashima itself, he's had a larger presence than King.
King has shown himself to be competent, and proactive in dealing with problems on the Beast Pirates side. He took charge of the situation with Yamato and again during Onigashima when the raid was discovered. He was also proactive in taking out Momonosuke and dealing with Sanji.
Despite all of this, it feels like he's had noticeably less panel time than Queen.
The Live Floor and game with the antidotes was orchestrated by Queen and featured Queen as the main antagonist.
Then we had Chopper vs Queen (which continued this chapter).
Even when the Live Floor was shown, we only got Chopper vs Queen and a shot of Marco, but King was nowhere to be found.
I feel like especially compared to Queen, King hasn't had the kind of prominence/focus/development you'd expect of an M3's main fight. I'm wondering if maybe he's not meant to be an opponent for the Strawhats after all.
I feel like even Ulti has been fleshed out/characterised better (and she's only Nami's opponent).
A major caveat would be that even if Zoro fights King, he wouldn't be Zoro's main opponent. All of Zoro's narrative is with Kaido, and King would just be a sideshow, so King doesn't need to be as prominent as Queen as been to work as an opponent for Zoro. King vs Zoro wouldn't be Zoro's highlight for the arc.