I agree to some extent, but I also think there's a clear stylistic element to riders in that. Froome always looked laboured. Nibali could look really smooth before looking down and suddenly pedaling squares. I think Roglic has been misread as riding easily quite a few times too.
Now with Pogacar, I'll say that I flat out disagree when people say he looked easy on Combloux, he rode away easily, and then he was struggling mightily just like everyone else becasue everyone smashed head first into that climb. Like he had his head on a swivel on the middle section of that climb.
Then for the rest, to me looking easy just means at the most that it's a controlled effort, which still can easily just mean a threshold effort, so it doesn't necessarily mean they can just go minutes faster. And Pogacar specifically is a guy who has an almost pathological need to show off so he probably does every indoor training in front of the mirror trying not to grimace.
Pogacar was going really hard on Combloux and definitely didn't hold back wanting to gain as much time as possible. I think most people said he looked easier the next day (Valmeinier). He slowed down at the end and effort intensity was lower (but it's also expected as the climb duration was longer). As you said, it could've been close to threshold (maybe somewhat below) and he could've looked good at this intensity.