Most overlooked aspect within those Commander debates:
Marco is not an ancient Zoan! People seem to understand the difference on an etymological level, but really don't get what it actually means.. or they simply underestimate Ancient Zoans, I dunno.
Ancient Zoans have that superb strrength, great recovery and insane durability, that was extra highlighted mutliple times.
Marco is an myhtical Zoan, means that besides the special quirk of his myhtical animal - the phoenix flame shockwaves and its regerneration- we have no reason to assume that he can hold a candle to hybrid King if we are talking about base stats. That's unless the mythical beast also has special quirks in relation to base stats or is in general just super powerful, which his phoenix fruit never got hype for in any shape or form.
The stat department is actually King's thing.
When Marco has used up all his phoenix flames it's likely that he will turn into a physically much weaker version of Hybrid King. And yeah i understand that Marco is a very likeable character, but if that happens, I fully expect King with ancient Zoan stats and his fire game to make quick work out of Marco.
I atleast can see it happening.