Before I joined this forum I thought I was a huge fan of lists and rating compared to most other people but here I find myself time and time again wondering what you are talking about. Some riders cannot be compared to each other. It's apples and pears. And sometimes there is no "true level" in comparison to which people underperformed or overperformed. Sagan has been an exciting rider, skilled, versatile, a charismatic character, a winner of many races, an athlete on the biggest stages of road cycling for many years. In my opinion that's his legacy and all these attempts at trying to figure out his "real" position in the history of cycling are doomed.
No, he's second behind Merckx.