I think that's the best way to look at it. Goff 42-20 with the Rams the past 4 years (and he was a big part of that .677 win pct.). Stafford 23-31-1 (.420) over the same timeframe. How would each have done with the other team?
For me I'll say this. If Stafford can be the top-12 QB he has consistently been, the Rams can maintain a top-10 defense (staying #1 will be a BIG challenge) and their special teams get back up into the top half of the league they should be playing in the divisional round next January. Beyond that? Crap shoot as it always is.