No, he did not have a HUGE drop off right after 2018, at least not as huge as you make it. He was 2nd in Vuelta, 8th in Flanders, 2nd in Lombardia (where he was probably the strongest rider). He was not very good in the Ardennes Classics back then, but that was also because he had initially planned to ride the Giro before his crash.Did you MISS the fact that he had a huge drop off after 2018? Yes he at best is at his 2019 levels. He is not going to EVER get back to his 2018 level. He had lost some of his explosiveness in 2019 and does NOT have it this year. That is obvious. In 2017 and 2018 he WAS racing against Alaphilippe. Right now Alaphilippe is NOT as good as he was in 2017 and 2018. In 2017 he BEAT Alaphilippe at Fleche Wallone. Yes it is EASY to make those comparisons and to use those years as a benchmark to his current form because it's obvious. If he has the form of 2017 he wins both races, if he has his 2018 form he likely wins at least 1 of the 2 and is on the podium at both. His current form is not anywhere close to the form he had those two years where he was virtually unbeatable. By the way, if he has competent form YES we should expect him to be in that front group, because that is him and that is to be expected. If he wasn't in the front group then his form is NOT even his 2019 form. Most consistent rider in the peloton for virtually 2 full decades, you EXPECT him in the front group if he has good form and you EXPECT him to have that form.
Moreover, if you resist that he will NEVER get back to his 2018 level, why do you always start making this comparison at all? After every race he is not winning this year, you start claiming, almost sounding derogatory, that he is at most at his form of 2019. Why is this relevant to his performances right now?
And, yes, in 2017 he was nearly unbeatable in Flèche and Liège, but result-wise he was also much worse in Amstel. I also disagree that we should definitely EXPECT him in the front group. Even prime Valverde sometimes lacked in making the right move at the right time tactically. How often has he been really strong in San Sebastian or Lombardia but did somehow manage to not follow the winning move? Even in his best years, there have been days where he would have stayed at Roglic's wheel today and then fought for 5th place in the chasing group.
And by the way. It is false that he beat Alaphilippe in Flèche Wallone in 2017. That was in 2016, when Alaphilippe was still far from his top level. In 2017 Alaphilippe did not contest the Ardennes Classics due to an injury and after 2018 he has always beaten Valverde in Flèche. So your argument that prime Valverde would beat prime Alaphilippe is completely unfounded.