I can only assume you never saw Marino play, underestimate the effect of rule changes, or both.Marino is my favorite player of all time and best passing QB in history imo.
That being said, the game is different today more than just inference rules. No doubt DBs are at a disadvantage but defenses are built longer and faster to deal with complex passing games instead of the physical running teams of their age. Many QBs of the current era have a mobility factor to their game to pickup first downs too.
No doubt he'd be a 5,000 club regular, I just think stretching it out to 7,000 and stuff is exaggerating too far.
In that era, QBs were fare game to be driven into the ground on every play. Receivers, literally, had to fight their way downfield, and PI was almost never called.