This assumes that employees are a fungible commodity whose price should be set by some efficient market rate, but that's not true at all.
Under the current regime, the setup helps top performers be compensated more highly, without torpedoing morale.
You can fantasize about a world in which the salaries are transparent and everyone has frank conversations like "Yes Jill makes 50% more than you even though you're nominally at the same level. Her compensation reflects her superior contributions to the company." But that's just not how it is.