You can easily apply numbers to rank quarterbacks. There might be some doubt as to who is number 1, but no one will doubt that Brady and Rodgers are in a different class than Cutler and Gabbert. You can partition them into groups of five, and assign a number ranking based on each group. You can choose any number system you want. Perhaps 1-5? And maybe within each class you can separate by statistical performance. Maybe that changes your scale 10 to 50? And maybe you don't like those numbers, so you move the minimum to 69? Now you have a scale from to 59-99.
So YES, you can use numbers to rank players. There is a subjective element to it, but it is clear that a player you rate as 99 overall will be better than a player you rate as 60 overall. Since you can use statistics to tie-break between subjective levels, your ranking can be a very good barometer.
And it is ALSO clear you can compare rookie players to veterans using the same scale.
And with that knowledge, you can easily compare long term trends. If you continue to group into these tiers, and notice that all the players in the top tier have much worse statistics than the players in the top tier did 5 years ago (after guys like Rodgers and Brady retire), you can reasonably conclude that the level of quarterback play at the top has dropped. It is there that you can decide that some in the top tier should be dropped to a lower tier, and once again you can use statistics to rank in each tier.
So yeah, you can easily see if there is a downward trend using numerical categories.
ADDED NOTE: Just because it CAN be done doesn't mean EA has done it right. Further, just because Super Stars SHOULD be rare, doesn't mean the end result of EA's attempts to make this so don't screw with something else.
Yes, BUT, if users are better at developing, won't they STILL have that advantage even if draft classes are better?
THAT is definitely a problem.