His overall level cannot, but him being clearly worse on the longest, hardest and highest mountain stage than he was the last two days does not bode well for how even an Evenepoel in great form would have gone on e.g. the Tre Cime stage at the Giro or the Loze stage at the Tour. I've said this before, but the Vuelta route was fantastic for him because it had zero big mountain stages and one HC climb, he's yet to show that he can go as well on stages of this calibre as he can on cat. 1 MTFs with middling run-ins and he'll need to if he's going to win a Giro or a Tour. Not saying he'll never manage (need a bigger sample size for that), but today does still count as a strike against him because it's still a disappointing performance when we correct for his form.
The more you climb, the more your W/kg advantage comes to fruition. (because you spend less energy following the pace of others).
Remco current output is at his max while dropping. Hence a longer climb,or more overall climbing is worse because he spends more time at max than the others.
if he misses 20W, thats like 0.3W/kg. So if they ride 6W/kg it is now extremely challenging while with otherwise its a breader)