But would you be okay, if you were a high performer, and you were being paid less than a colleague barely scraping by.
Of course, but the fact remains that there is no “equity” in a free market. The company can pay anyone any amount it wishes whether or not it is “fair”. Don’t like it - leave.
The free market is the only true means of assessing the value of anything, including that of yourself as an employee.
Without knowing why the boss would pay an underproducer more than a producer, I can’t judge the entirety of the situation.
When my father had a heart attack and went through a triple-bypass surgery, his boss very kindly paid him his regular salary while he was unable to work. The condition was that my father was to never talk about it to the other employees. Was that fair to the other employees who were producing, while my father wasn’t? We didn’t know if he could go back to work, and neither did his boss.
If I don’t like being paid the same or less than someone I think is less productive is a moot point, because that’s between the hirer and the hiree. If I don’t like it, I can look for another job.