I honestly think he's hit his peak, or about as close to it as we'll see him. And even if i'm wrong, i'm not so sure whatever he can still gain, will matter all that much. Pogacar is only going to get better and get better support. Carapaz is still going to get better (and get actual support), Dumoulin is a year younger, and he hasn't been "worn out" either and is sure to return significantly better than in 2020. Bernal is going to come back better. Carthy, Mas, Evenepoel, Hindley... all have a much bigger chance to leapfrog him, than him finding a so called magical "other gear". Having seen him winning plenty of one week stageraces comfortably, i can't help but get the impression three weeks is seriously "stretching him thin". I also think he isn't the strongest guy from a mental point of view.
In a sense he's caught between generations, and in his case, that may very well have been his luck. Froome, Thomas, Nibali... are all done (not to mention Contador etc), but Bernal, Pogacar are much younger and already hit a higher peak, caught a bigger fish than him. Even if he still has a small margin of improvement, there are guys waiting in line, who still have a much bigger margin of improvement while they almost or already surpassed him. It may very well have been his only real shot at winning the Tour, and i wouldn't bet my house on him ever winning any other GT either. Just like the window of opportunity has closed for Landa, Bardet, Pinot, Yates and others in their late 20's to early 30's.
In any case, i sincerely hope we get a less formulaic version of Roglic in 2021, because he's bored the snot out of me this year. In fact, imho it is an extra indicator there is no other gear. The scripted manner in which he rides (or the team for him), seldom if ever (since becoming an actual GT GC contender) attacking further than 400 meters away, tells me that is all he can spare in order to get the job done. Barely and in unspectacular fashion.