Calling Rob Gronkowski the greatest tight end of all time is like calling Darrelle Revis the greatest cornerback of all time. Better than anyone in their prime, but too brief a prime.
Revis is a queynte, but I think there's always been far more talent at the cornerback position than tight end.
It's only fairly recently that we've seen the tight end position evolve so much. That the talent of the tight end position should be dramatically elevated in the future as the position continues to change.
There's a reason why the average #1 tight end makes way less money than a top corner or wideout