what you can demonstrably show is that Goff's stats are worse.... what is more difficult, and what I'm getting at, is whether that is all on Goff or not? You're saying it is. Well, that 'could' be, no doubt... but I'm thinking other factors are involved except perhaps in this way:
I think it's far more likely than not that Goff, since his rookie year, has been asked to do more and more.... and not season by season but rather game by game. I don't see it out of the realm of possibility that Goff has plateaued on that learning curve so... what we're seeing today is not entirely, if at all, regression in Goff's skills but rather an inability to make decisions since he's been called on to 'think' more. IOW.... if he had less to think about I don't think it's impossible that he'd be playing more like the Goff of old.