How's he the weakest when he is the most skilled one among them? How is Marco stronger than him? Now we know that Kizaru just trolled Marco and Big Mom choke diffed him. At least Post WCI Luffy was taken out by TB.
There are currently 3 known first mates and one of them has CoC, awakening, FS and will overtake his Mother's crew. Good, Marco has some redeeming qualities since he also leads the WBP now but King only gets carried by his genes and this dude legit has no future left whatsoever.
It's even more likely that Vergo reappears with the Axolotl fruit than King whose future got crippled by Zoro and Aramaki.