We go through life making a lot of guesses and utilizing a lot of prior probabilities. Work history is, in my experience, one of the stronger signals available to us.
If an employer initially pays an employee less due to less track record, then finds out the employee is as good as other employees, and does not adjust the pay, then that employer is stupid and will eventually lose the good employees to places with better management. Assuming employees have access to sufficient labor pricing data and can see they can earn more elsewhere.
> But that shouldn't be a >5% difference.
What is the basis for this cutoff?
> Are you going to tell me that despite performing the exact same job and actually performing it objectively "better" that I should have made less money?
You should have made whatever the maximum you could negotiate. If this employer did not want to pay you more, you should switch employers. A good employer would have paid you much more than the others.
>This is the kind of stuff that routinely happens to women.
No, your example is bad management incentivizing bad employees and turning away good employees.
Women being paid less due to being women is illegal discrimination.