My take, for what it's worth, is that a seniority list might be fine for taking care of those kinds of adminstrative details, but shouldn't apply to things like promotion to command. I'd rather have the most capable and appropriate promoted first, rather than simply the one who's been there the longest. In that respect, seniority lists encourage a culture of entitlement rather than one of earning advancement.
Of course, this is predicated on the system being fair and a genuine meritocracy. The people deciding on who gets promoted have to be competent to make that decision and base it on fair and known criteria, and not let it decend into cronieism. There will always be doubters of any system, and one has to have some trust in the people deciding on the merit for promotion, but I still think that can't be any worse in promoting the untalented than a "who's been alive the longest" method.
The military, for instance, have a mixed system. You are only eligible for promotion when you've reached a certain level of seniority, but you still have to pass a promotion board who decide on your suitability. You still get some wasters promoted in that system, but it does tend to weed out the truly unfit for command.