You're severely underestimating it.
Onigashima is surrounded by a mountain range:
Y'all should've realized that Onigashima is an extremely small ass island when Marco himself called it small or when Kaido imagined I'd perfectly fit into the capital.
Busting out actual calcs of the island is absolut madness since you can't depend on Oda whatsoever to stay consistent with it.
All we know is that the Flower capital is the smallest region of Wano and the entire island of Onigashima fits perfectly into that.
It's Mountain range cannot be held to the same standard as we're used too from other island.
King's attack did a lot of damage but it ain't even close to KKG level, that's some next tier wank.
Rooftop Zoro is a significantly stronger swordsman and he was sent flying by just one of them.
Send flying is not defeated. We don't know how physically strong Smoothie is. All we know is that Oda has called her strong.
Your issue is insisting that King is in the same class as them when he has everything Marco has, but also:
- Zoan form durability superior to Kaido's dragon scales
- Offensive prowess superior to Rooftop Zoro
- The lethality of swordsmen
- The stamina and recovery of an Ancient Zoan
King is of a higher calibre than Marco.
King is in the same class of Marco and Katakuri, he was never something else. Portrayal is always more important than feats. In the end, King is "just" a right hand like Marco or Katakuri. The special person amongst the Beast pirates is Yamato because she's playing the Ace, we've a pretty clear understanding of were King exactly stands. It's the same position Marco and Kata are/were in in their respective crews.
His Bounty is proof of this. If he had a bounty above Luffy I'd wholeheartedly agree with you but there's a reason he's so close too Marco in more then one aspect.
Marco, King and Katakuri all play in the same ballpark.