He would go against the defending champion, who has been working towards this goal and comes 100% prepared, while he (Evenepoel) did not work towards that goal, already peaked for LBL 2 months ago, did not have the best preparation, missing the ideal altitude camps, not having done any recons etc. Is it impossible for him to win the TDF? Maybe not, maybe Vingegaard crashes out, Pogacar also didn't have the best prep with his wrist, etc. But chances of him winning are slim at best. While if he goes to the Vuelta, he has a 50% chance of winning, in case he doesn't crash or get sick.One would take the Vuelta win for sure, but neither is a given. One could always make such assumptions and thus never go to the Tour. At the end of the day I believe a little sickness should not derail the whole season and therefore he should make the adjustment to go to the Tour after racing just 9 days at the Giro.
What happens when he goes to the Tour and crashes out or gets sick again? Then it is a completely wasted season. Because then he won't get ready for the WCC and surely can't peak for a 3rd GT in one year. Let him go to the WCC and then defend his Vuelta title, and come back next year fully prepared to tackle the Tour.