As a recent ex service pilot with over a decade command experience and recent Longhaul Commercial FO convert, I would say that the seniority based system makes lots of sense. I regularly saw the nepotism talked of above previously and it turned my stomach. There are plenty of opportunities in a larger legacy, seniority based company to make your mark outside of 4 rings. At the end of the day, they are the T and C you sign up to, for significant long term benefits and an equitable time based seniority system.
Plus I don’t need 4 rings to influence the outcome of the flight in a positive and significant way. My way of using my skill and experience is to do so in a way without undermining the captains command authority.