How about from a play calling perspective? Keenum can seemingly run a wide open playbook. He can run 3 step drops, he can do 5... he can go shotgun and stand in there.
Its easier for Shurmar to go full throttle with the playcalls, and easier for Keenum to establish the rhythm, when Reiff has been a wall on the left side. We can do what we want, when we want, and rarely need to scheme protection to the blindside. Shurmar can scheme and attack defenses how he wants and Keenum is comfortable and can get into a groove.
Put in an average or below average guy there at LT, and we probably can't run such a WR heavy passing attack. Or at least execute them as consistantly as we are now. There are probably more 3rd and longs and punts. More plays instantly collapsing where we are forced into bad situations or into 4th downs.
Reiff certainly makes Shurmars job calling plays smoother.
I could settle on Case being "MVP" as his stats, his play, his position (hey, he touches the ball every play), coming off the bench after some bad injuries and little hope. Its hard to imagine any other guy leading this team to where we are at. Promising players get a shot and wash out of the league all of the time. Every team in the league has a guy with "potential" who dont create their own oppertunities.
Reiff will be a cornerstone for playcalling and whoever is under center for years to come. He's the "better signing" on those conditions i'd say. If/when Teddy/Sam hit the field again, we'll be thankful he's playing LT. We'll rest easy all offseason about the QB protection, and hopefully this level of play simply carries over to next year.