Realistically I think for what his expectations are he proved himself this year.
Goff wasn't shipped over from LA along with a multitude of high end draft picks because he's one of the best in the NFL. He isn't expected to carry a lesser team on his back, or have some magical run to the postseason while throwing to guys like Kalif Raymond and Tom Kennedy. He was and is expected to hold his own, not turn the ball over excessively, and do enough to allow for observation of player development at skill positions. Largely, I think he's checked those boxes if you evaluate him on the whole instead of cherry-picking his worst games.
Despite being frustratingly dink-and-dunk at times, he is clearly a leader, has more than 2x the number TDs to interceptions, and we have seen guys like St. Brown emerge as a real potential #2 Wide Receiver for this team. In the sense that this trend needs to continue as we likely add a future #1 receiving threat this offseason, I agree that he needs to continue to prove himself. But I would not discount what he has shown us this year.
I agree with pretty much everything else you have said though. To be clear, Goff is not the QB of the future (at Hart 😉), and the answer to that problem is not panic buying a bad QB while there are holes across the roster. I would really go even further and say if we don't see the solution with the Rams pick, don't bother. If they are a solution, a team that finishes better than the Rams (Indy and Green Bay come to mind) would likely select him anyway, and two upper-echelon 2nd Round QBs in the last 30 years (neither upper-echelon with the team that selected them) is enough data for me to say that it probably wouldn't work for Detroit either.