It isn't.
But equal pay for inferior effort is a good thing (for employees).
Meaning, if your firm pays market at 1900 and pays more for more, then good. But if they pay <market for 1900 and you need to bill 2200 to get a market bonus, that's bad.
i hear, but it depends on a bunch of factors. at my place (with some slight changes in the thresholds) what you refer to as bad is the basic setup, but if i can get away with a full salary and an 1800 hour year with no complaints, thats nice too.
in addition, at many second tier biglaw places i believe that u can get a bonus anyway if u prove your worth/value (i.e. once you've already put in a couple of years, the thresholds can be bent a lot).