This has historically been the way van Aert has been able to beat him. Driving the pace up... continuously and unrelentingly without giving van der Poel the ability to recuperate. If he (Wout) did that, if he let the pace slip somewhat, he could basically start over, because it 's enough for Mathieu to recharge his batteries. This is why van Aert beats him at courses like Valkenburg or Dendermonde, where he literally ripped van der Poel to pieces. Those were courses that were so hard, and technically within van Aert's skillset to power through without losing time on technical sections. The issue is, that cyclocross by nature, is hard to keep the pace high constantly, because there are a lot of twists and turns, obstacles etc, so on most courses it's practically impossible to keep the pace high non-stop. And that is exactly what van der Poel excels at, short burst after short burst.
In layman's terms, van der Poel has a set of above average sized batteries that recharge very quickly. Either you need batteries that recharge even faster (basically impossible), or you need bigger batteries to outlast him. That's why he doesn't cope well with longer climbs. I also believe, had Strade been as hard as last year (11 people within 10 minutes in 2020 vs 56 people within 10 minutes in 2021) that Mathieu would not have won this race.
To compare that to another outlier, a fine example would be the raids in Binckbank Tour (van der Poel) and Poland (Evenepoel). Both doing a solo against a stacked field of chasers. Both attack from a small group around the 50k mark and in both cases there already had been some action before that. The difference is, at that moment, van der Poel already has a 1m10s gap on the peloton that will blow up shortly after (40-25k, at some time his lead has extended to 1m35s), meaning his chasers (SKA, Naesen, Colbrelli, Küng...) were already at a large deficit before the chase started. They should however, have been more fresh. So how does it pan out? From the 1m10s gap he has going into his raid, he only keeps 4s at the finishline. Compare that to Evenepoel, who attacks at 51k from the group of favorites, and has no margin on his chasers going into his raid. He extends his lead to 55s and keeps this gap fairly stable for most of the effort on a much harder parcours (longer climbs). However, as the race goes on, in the final 15k, Evenepoel pulls away an extra minute. So, van der Poel starts with a large bonus (max gap 1m35s) and wins by 4s. Evenepoel starts without a headstart, and wins by 1m50.
I'm not posting this as a plea to prove that he is most definitely not doping. Or to show that he isn't that exceptional. Just to explain where his strengths and relative weaknesses lie and how those differ from other riders.