I always believed Marco was a Strong High Tier but i think he is indeed Admiral Level
I think People should rework their Power Leveling, Characters who stand out among Groups are indeed Near-Admiral Level
Aside from Agreed Upon Top Tiers, Characters who imo can Fight 2 Commanders like King & Queen are:
Luffy - Zoro - Sabo - Marco - Magellan - Lucci - Katakuri & Stronger Half of Shichibukai
Luffy is Future Pirate King while Zoro is Future Greatest Swordsman & they are both performing well against Yonko
Marco just proved himself here
Sabo is No.2 of Revos Army & can fight Two Admirals with Help of Three Revo Officers who seem to be Ivankov Level
Magellan is considered Warden of Hell & everyone fear him, he can one-shot in seconds someone like Ivankov & even Shiryu who is Strongest Commander of BB Pirates doesn't dare fight him even though he is considered near equal to him
King & Queen seem to be like Cracker & Smoothie & Katakuri is portrayed as Superior, as simple as that, he clearly stands out
As for Lucci, i think people underrate him so much, but the guy is considered a Legendary Fighter among Cipher-Pol & even Pre-TS Lucci was considered superior than Vice Admirals & All Three Great Powers found his Loss Shocking, so imagine Post-TS one
As for Shichibukai, Weevil & Prime Kuma, Prime Moriah, Doflamingo ... etc are clearly a force to be reckoned with
Jinbe in Land is YC Level but Jinbe is a Fishman & we know that a Fishman underwater is much much stronger than Land Version
Also Marco's Performance Today showed me that Rayleigh, Oden & Beckman are indeed Yonko Level