Unequal pay is going to be present in any environment barring rigid pay grades like civil service or unionized positions. One of the fundamental things about most white collar work is that you are supposed to be compensated for what you bring to the table, not necessarily how long you have been there or even your position. It is not uncommon , for example, in tech sectors where a tech superstar might make more than their manager, and someone who is the manager of a development group will likely make a lot more than the manager of office support staff.
Most companies do have pay levels for certain levels of employees, a range, that they use in judging where someone is. The problem with that is in most organizations, they are trying to get away from structures where there are rigid grade levels a la the civil service, they also are running flat management structures so titles are not necessarily a way to increase pay, not to mention the old dilemma about promoting employees to manager to get them more money when they can’t manage or don’t really want to.