[happytoexplain]

Fully half of your post is a sarcastic rant.

>why not determine what an employee at a given level is worth to the company, and pay that amount to anybody

Because the same salary may be worth the same amount to the company paying it, but it is not worth the same amount to different people receiving it. Among two equally valuable people, one may accept and one may decline due to salary's differing value to them based on environmental factors. This is obvious to businesses, and is generally accounted for (fairly or unfairly).