He was able to drop everyone (except Pogacar) multiple times. He looked superb following Pogacar on most bergs. He only cracked on the last Kwaremont, which may have had something to do with following Pogacar relentless accerelations on every berg, don't you think? Do you know the term cumulative fatigue?
I'm not denying that an illness can hamper your fitness though. Yes, it could've affected him. But we really don't know if the outcome would've been different. Being sure of that is a very naive approach.