One look at OP.GG is all i needed to know you got the entire thing with "fiora going grasp" from either diamond or higher up.
And strangely enough, conqueror is still the most picked keystone by a margin of 70% of all games even in diamond as shown by the very site you linked,......
How very peculiar, i could have sword you wrote something on the lines of :
{quoted}
uhh tanks with grasp beat almost every top laner (cause conqueror is weaker in lane) any day
even fiora goes grasp
Evidently the overwhelming majority of Fiora players, even in diamond, picks conqueror so it cant be weak no matter how you seek to claim it.
oh and if looking at master, challenger and one tricks in addition you´ll notice that despite fewer games played grasp has worse winrates in all 3 ranging from roughly 2-4%.
You sure you havent gotten conqueror and grasp confused for eachother?