Aaron Rogers is a HOF QB. A rare talent. It is totally unfair to make any comparison of a 3rd year QB to Aaron Rogers, more or less implying that it is necessary for Goff to achieve Rogers' status and level or a certain degree of failure or underachievement or lack of work has occurred.
Not a lot of NFL QBs in their 2nd year have achieved a 100 QB rating as did Goff, especially not in a brand new offense with a brand new coaching staff.
I don't know what Goff will ultimately be; but whatever it is it won't be Aaron Rogers' like because he doesn't have the same attributes as Rogers.
However unless Goff was a 16 game fluke, he's already a Pro Bowl QB and there's no reason to think he ought to regress. Although it is certainly not impossible.