Sawyer7Mage made my exact point on Marco v. King. If you have to decide between Marco or Zoro for King, it's Zoro. One Piece is the SH story, not the WBP story. There is no one left for Zoro to fight.
As for Marco, will he and King clash aerially? Most certainly. It might even happen in the next 1-2 chapters when he saves Momo. But Marco DEFEATING King, is a whole other subject matter. Luffy clashed with Pica too, it doesn't mean he was going to take him down.