Earlier quoted context omitted.
> as her sub-employee are risking the most severe of all offenses - asking for more than what your supervisor makes. This is a flawed philosophy. As a manager I have had a few critical pulling in higher salaries than my own. If you are a superviser who is artificially holding an employee back from reaching their full potential (seeking compensation that matches the demand person's talent in the open market) than you…
you are argumenting from an optimal-employee-perspective or what you might choose to call it. Fact is - even supervisors are humans and 90% of them will be hesitant to have somebody "under" them while making more or as much money. I fear that's just a fact.
EDIT: My main responsibility is to keep the team happy and productive. If this developer would leave the team our productivity would drop and we wouldn't achieve our goals we set for ourselves this year. It would have a direct impact on my bonus as well and it is in my highest interest to keep great people at every possible cost. If I think I don't earn enough then I will have that chat with my line manager, but I will never try to destroy my team based on some personal ego crap.