Baloise Belgium Tour or Adriatica Ionica wasn't exactly against Thomas, Lopez etc. San Sebastian was him vs domestiques. And once he has a gap, it's hard for anyone to bridge, especially when domestiques are burnt by then. If he's in full ITT mode once he's got a gap, that's when it becomes a problem. I doubt worldclass climbers will get dropped on a 6k climb.
I wasn't extrapolating that, or i'd be talking about 25-30 seconds. I remember a few late attacks by Thomas in 2018, where he took more than 10 seconds on rivals in the final 1k. Those rivals in turn were already more punchy than Evenepoel and could in turn easily take up to 10s on him. Now, these climbs may not see such gaps, i don't know. I'm not talking in absolutes, but guys like Thomas, Kwiatkowski who could still be there on the top of the climb, could do enough damage to become a big problem in the ITT.
EDIT: Pogacar took 19s on guys like Poels & Pauwels last week, in only a few hundreds of meters (the three-way sprint with Valverde & Teuns). Knox finished at 8s and according to some people here, he climbs better than Evenepoel. I'm not saying it will definitely happen or that it will definitely be 20s, but it's also not out of the question imho.
Yes. If Dennis climbs as well as in TDU he'll be a huge problem for anyone. On the other hand, like you said, the question would be how his ITT form is (or is it the bike?!).