All we do here is normalize employee comparisons at the employee-employee level, and not at the employee-corp level thus *keeping our working class fighting itself* while the owners ensure we help them pay as little as possible for their labor.
You measure it the same way that you measure the relative difference in compensation that a manager should make versus a SWE. You make a subjective assessment. Why is such a subjective assesment OK in the case of manager vs SWE, but not OK in the case of SWE vs SWE? Both assessments are equally prone to mistakes and difficulties of the type you are talking about.
> All we do here
Convince me of this, because to me, this is necessary to being fair and just. As an employee, I would feel ripped off if I am clearly doing more quality work than a colleague, but I am being paid the same. It's unfair, I am de facto doing work that's uncompensated if I am doing 2*X but am being paid as if I was doing 1*X, which is de facto someone stealing money I rightfully deserve. In effect and outcome, it's no different to wage theft being done to me, due to the fact that half of my output is de facto uncompensated. And let's be real, sometimes it's super obvious when one person is more productive than someone else, even if in other cases it can be hard to measure and separate the contributions of two individuals, and even if in other cases those perceptions are distorted due to narcissism and information asymmetry.
So by this logic it's fine for a manager to be paid 2x more than a subordinate, presumably because they're 2x more important/valuable/scarce/productive/whatever, but it's not fine for a software engineer who is 2x more productive to be paid 2x more than the less productive software engineer, all because it's "the same role", and such categorisations are arbitrarily chosen. Assuming I'm not strawmanning you, I don't see why this makes sense.