Neither rider were top end at GTs, correct. And so their abilities at GTs are less important in assessing them. They are great one day racers, great all rounders, great short stage racers and pretty strong but by no means great GT GC riders. Kelly was clearly better at all of the parts of the sport that put them both among the greats! Even when it comes to season long bulk winning of small races, another big important strength of Valverde, Kelly was simply better.
I think there's a distinction to be made between judging who was the best rider vs. the best all-rounder (a distinction which, to be fair, I didn't make when starting this thread). You think Kelly's dominance in monuments and other one-day races more than compensates for his lesser results in GTs, making him the better rider. I can respect that, but being the better rider doesn't necessarily mean being the better all-rounder.
E.g., I would say Froome and Contador are better riders than Valverde, because their dominance in GTs compensates for their lack of results in other races. But no one would say that Froome and Contador were better all-rounders than Valverde. You might say Usain Bolt was a better athlete than anyone who won the decathlon, but any decathlon winner is more of an all-round athlete than Bolt.
At the highest level, Nibali. Definitely up there.
Agree with that. Definitely better than Valverde at GTs, to the point where he's almost in the conversation as the best GT rider of his generation. Not quite, but definitely up there.
As for monuments, Valverde has been more consistent with 11 podiums in 30 tries, vs. 5/26 for Nibs (who has more time left, though). Valverde also has a far more impressive record in shorter stage races,
I'd put Nibs in the conversation with Valverde as an all-rounder, because he's shown more talent in one day races than other elite GT riders have. If he concentrated more on them and less on GTs, no doubt he would win or at least place in even more. You can't say that about Froome and Contador, and you can't say Kelly didn't concentrate on GTs.
But again, this underscores the point about specialization. You don't expect GT riders in this age to contest a lot of one day races. That's what makes Valverde's record so unusual.