I like this thread but then every time I look at the poll I flinch for a moment because Froome and Vingegaard were included.
I think what one really has to distinguish is who is the best descender and who is the, let's say, most legendary descender. I think Nibali has to hold the title for the most legendardy descender of his generation, even though I'm fairly certain the likes of Mohoric, Pidcock, Sagan and some others are better than him. But in the field of lightweight gc riders, Nibali simply stood out much more than any of the other guys among their respective peers. Nobody in the current peloton has either won nearly as many big races with their descending nor was part of more famous downhill attacks. And yet I still get sad because he didn't also attack on the Mortirolo descent in 2019. Oh well...
I also think people underrate how big of a role your physical strength playes while descending. You regularly see that guys who are completely dead on top of a mountain lose additional time on the descent, not because they are worse descenders, but because they don't have the legs to accelerate out of hairpins. That's how someone like Nibali loses time to someone like Pinot on the Civiglio descent in Lombardia 2018. I think this is also why some people call riders descending "inconsistent". Some daredevil descender goes over the top of a climb in the lead group, so people automatically think he should gap the group on the descent. But if he only hung on for dear life on the ascent, he's not gonna have the strength to gap everyone on the descent, regardless of his skill level.