ANY QB from "back in the day" would be BETTER in today's NFL.
WR's that are bigger, faster, and stronger that are allowed to run their routes untouched... then aren't allowed to get hit like they were before.
Not worrying about getting whacked in the head like they did in the past, etc...
Marino would probably put 5K yards way in the rear view mirror. I think he'd be pushing 6K yards in today's NFL.