You should be paid as much as your skills, and the uniqueness of such, commands. Your employer should pay as little (or as much) as they need to in order to obtain and retain the quality of employee they desire.
While your position is "based" on solid ground, the problem comes from inconsistency
within the company. Your post touches on yet another (smaller) piece of the puzzle. Driver retention. According to your thinking, and other's thinking within the company, turnover (or lack there of) plays into this as well.
Because one location has more loyal employees that another, that (loyal, dedicated) location's workforce might not see the same gains as another location, just down the road? This solely based on low turnover? This is one reason why, there are times when workers MUST do what they can to improve the
current workplace.
We are beyond comparing ourselves to the top dog in the industry. We can now make the case, in some locations, comparing our compensation to traditionally "lesser carriers". In my location, the disparity exists
within the company, as well.
You might not like my method for seeking redress on this, that is fine. Just know that every single path within the Company has been explored, tried, and exhausted. Currently, the hard part is being patient enough to see if/when the company will respond.