I do think it’s a fair criticism that Oda failed to hype King as much as he should have.
Compared to what we’ve seen from Marco and Katakuri, and considering the Beckman databook wank, King seems extremely underwhelming.
Btw, there is a pattern here. Oda always does this.
PH/Dressrosa -> Took out Vergo before Dressrosa started
Wano -> Took out "Joker" before Wano started
WCI -> Took out Katakuri before facing Big Mom
He always takes out the top subordinate before the main arc where villain is defeated.