There is some merit to this. He is not a game changing QB when the chips are down. He cannot will his team to victory like a Wilson or Brady. But Wilson's or Brady's are truly one in a billion.
Goff is not that. He is proving to be a gifted thrower, good person and QB, and a good face of the team in terms of working hard, new stadium QB/image, Super Bowl on his resume, etc. But has he hit the ceiling? Scary to think, yes, he has.
But if he does not have a good OL and receivers and a running game, he is quite frankly average to below average and because of his second contract, being paid as way above average as second contracts are designed.
Now, what if they waited and franchised him in 2020 and he was still average, do they pay him maybe $120MM guaranteed as the cap goes up or move on? Intriguing question with no answer now...