You look at the box score and draw a conclusion. Adams only had 50 yards, the line isn't that good. What a formula like S&P+ does is take every individual play, weight them against the opponent, throw out garbage time, and it comes up with a number. The numbers say the lines have been quite good, which makes sense because we've seen a number of them go on to the NFL.
So we have:
-players going on to play in the NFL as high picks
- good rankings for the line as a whole
Maybe your hypothesis is wrong.