First off the upgrade that Stafford gave the Rams pre-snap in identifying threats was the single biggest difference, because Goff in 2020 had regressed so badly there. That alone was worth the change because Stafford was the best in the league vs extra rushers.
But the downfield penchant for big plays is really the reason for the change. Which, when you consider that throwing deep requires everything else to be in alignment from those pre-snap reads to getting through reads quickly to being able to accurately predict the safeties and read their intent. Plus as we saw on the final drive in the Super Bowl and all through the playoffs the value of Stafford's ability to play eye games to control the safeties can get you open wideouts at crucial game moments when you have to make a play.
Rams in year two of Stafford/McVay are going to be an enormously tough out for opponents. I just hope they are aggressive in restacking this roster on the OL and secondary in order to give themselves the roster they need to do this again.