I was one of those blokes that thought King was equivalent to the Mama's Boy of Candy Island. With the new information we were given I've updated my opinion on King, and now I believe he may be YC1+, if not outright in the Low Top Tier.
You shouldn't devalue Zoro's performance against Kaido and Big Mom, but rather simply admit that King is more impressive than we'd assumed previously.
If you want to point fingers, blame Oda for making King do absolutely nothing until recently.