They were clowing King hard until he became Zoro's opponent. Now they boost him to the moon lol
To be fair, you can only blame Oda for that.
The fact that Oda offscreened his victory against Marco and his second easy victory against Cook, on top of shafting him (and Jack) to irrelevancy during the raid in favor of super important people like Momoron, Otameh, and Raizou (something that didn't happen to, say, Katakuri in WCI) hurt his portrayal greatly (and hurt Jack's even more).
King being underestimated is due to Oda's decisions, not the fault of the readers. After all, readers can only infer from what Oda shows them. Also, "benefit of the doubt" can only be given for so long. The readers are not responsible for Oda's decisions.
Suddenly king is that strong even though he didn't do anything to put him that ahead of kata or marco, pushing zoro doesn't necessarily make him strong it can be that zoro is just not as strong as you thought.
Read my reply to
@Van.
Also, if we go by leaks, King is pushing the Supernova with the best portrayal in Roof Piece to a power-up.
Be an adult and give credits when credits are due, man. Zoro is exceptional, so King has to be, too, to push Zoro this far.