But then if it gets low diffed by enemy doctors like Chopper... Well, now that’s a whole section of his army gone to the enemy side because of spite
Well let's see what it took to deal with Queen's Ice Oni plague after an extended period of time :
1. Top Tier Medical expertise from if not the best, one of the best in the One Piece world in Chopper
2. Perfect counter from Yonko First Mate who can provide large scale AoE healing flames that can buy said elite doctor the required time to work on a cure
3. Already having the antibodies so that said doctor doesn't have to start his work from 0
Without Chopper everyone on that floor would be fucked. Without Marco specifically having the perfect counter, even if Katakuri or Ben Beckman would have made an appearance everyone was still fucked, cuz they'd have nothing that works to hold back the effects of the plague.