I'd put Pidcock at 80% and then the field at 20%. Really no reason to even have the WC's here in the US. I doubt even 1% of Americans know who MVDP or WVA are, let alone Piddy and the rest of the field.
Considering we can't have the race 100 times to see how many times Pidcock would win, it's a bit stupid to discuss it, but objectively speaking there is no way Pidcock has an 80% chance to win, not even close. He will not have help of any other countryman, he will not have help of any teammate. He has none. While there will be a big Belgian squad, and even if team interests play a bigger role, then you still have Aerts + Van der Haar who will work together, and Iserbyt and Vanthourenhout who will work together with possibly Sweeck. Then there is Hermans and Van Kessel, though i assume they will not really play a big role unless Hermans goes on an early rampage and everybody stays in Pidcock's wheel waiting for him to close the gap. Pidcock did win a few times lately, but not that dominantly in the slightest to claim he has an 80% chance at victory.
He was only marginally better than Aerts in Herentals beating him by one or two seconds (over one minute down on Van Aert). He was only 16 seconds faster than the mighty worldbeater Wyseure (i bet you 've never heard of him) in Gullegem. In Hulst he was 12 seconds faster than Iserbyt. In Baal he finished 19 seconds ahead of Iserbyt. In Zolder he had to beat Iserbyt in the sprint after having had to chase after him all race. In Dendermonde he got blown away and finished behind Sweeck, Hermans, Van Kessel, Aerts, Vanthourenhout. In Namur (one of the more prestigious crosses on the calendar) he was the big favorite but got clobbered by Vanthourenhout. In Rucphen the entire top 5 finished within 15 seconds. In Val di Sole he finished well behind Vanthourenhout.
One less than stellar day, one flat tire, one too many crash, a bad start... and it's out of his hands. No teammate to bridge a gap, and it will be all against Pidcock. Even if all goes well, the margins by which he beat the others who will be present at the WCC are in no way so extreme that you could make a claim that extreme. When he finished ahead of the others, which wasn't even always the case, it has been within 0 to 20 seconds. On any course imaginable, there will be one or two who can potentially beat him. He is not "part of the big 3". He is simply "best of the rest".