Some of the commentary seems to be he is on the field more, which makes him better. Not exactly earth-shaking, as you cannot be better from the bench.
I don't view Gronk as lesser, just, as some have noted, he is the only guy on the offense for much of this season who needs defending. Kelce is not the lone weapon.
I thought Kelce was more of a blocker than Graham, but nowhere near Gronk's blocking. As a receiver, with all being equal in terms of weapons on the field, I don't think he is better than Gronk.