Here is the other thing about Goff....we've seen who he is, many times over. With an elite supporting cast, well....the best game I've still ever seen was Goff against the Vikings in 2018. Pretty sure it has an argument for best QB'd game ever, because IIRC its the most pass attempts of all time to have a perfect passer rating. That was never in doubt.
The problem was when things broke down. Kupp got hurt, the OL took some hits, Gurley's knee.....in 2020, we had the #1 defense in both points and yards allowed. We had Cooper Kupp and Robert Woods, healthy. We had the one good year of Cam Aker's career and a top 10 running game. A QB can not ask for a better supporting cast top to bottom than that.
The season after, we swapped out Goff for Stafford and the running game fell off with Akers achilles injury, the defense regressed, then in the Super Bowl, we were down to basically Cooper Kupp and Brycen Hopkins on offense.
Then, even after that, we saw Goff melt down at home in a divisional round playoff game against a mediocre Commodes team.
If you just compare stats, Goff will always be right there. He was before the trade happened too. Its not about that....it never was. Its about being able to carry your team when things are not ideal, and being able to perform on the biggest stage. Stafford isn't perfect, but in those he destroys Goff.