By "quality" I mean "overall quality" (OQ). You know, the number in brackets, not percents and stars, which are relative quality. Stars are different on every level: 5* on level 3 equals 4* on level 4 or 3* on level 5... That's why it's relative. OQ, on the other hand, stays the same for all levels.
By the way, do you know about 20% relative quality loss on promotion? Your 100% players will become 80% after the season ends, if you get promoted to the next level.
Wage is "glued" to OQ, and contain no new information. I mean, if you have, for example, a player with OQ 111, his Wage will be ~9.8M (or slightly bigger) no matter what. Therefore, there is no need to use Wage. Being a FT is about having certain Value for certain OQ (thanks Nik for
the summary). Dividing Value by Wage gives you nothing new.