Nobody is saying McVay isn't much better than the Fisher/Schotty duo. (Although, I think Schotty was an average OC for us. The guys who came after him made him look like a genius.) But the fact is that when we traded Sam, he hadn't played a snap of regular season football in over 1.5 years. He had torn his ACL in back to back years. Fisher had also had five years to stunt Bradford's growth. Do I think Sam could have been an above average starting QB had he landed with a better coach and stayed healthy? Yes. But his career played out the way it did.
Say what you will about Goff but he just finished his fifth year (like Sam had with Fisher) and has two Pro Bowl appearances, four winning seasons, a Super Bowl appearance, two 100+ passer rating seasons, led three top 10 offenses, and has led his team to three 10+ win seasons. Sam had none of those things. And unlike Sam, Goff has proven to be quite durable. We're talking apples to oranges here.