One of the problems in todays industry is the seemingly reducing T & C's. Something that the seniority system does nothing to combat. In fact it makes it harder to resist, since most people would usually vote with their feet if treated badly, but with the seniority system you could lose too much.
Loyalty should work both ways, something that companies like Ryanair should learn. (If there was an argument for a strong pilot body and something like a seniority system that would be one!)
As I've said, I don't think seniority is perfect, but it does seem to be the best that is available at the moment, but it is by no means perfect. A hybrid system that took length of service into account, but also took competance and further training into it.
Younger, less experienced pilots are more likely to be "anti", simply because they have less to lose. It doesn't make their comments less valid though.
wrt, comments about management structure. As an F/O you fly everyday with your immediate line manager, the problem is that this person is different all the time. I think this structure is one of the problems in this business and one of the prime causes of the "them and us" antagonism that can go on between flight deck and more senior management.
There is no/little relationship between "head office" and flight deck unless there is a problem, which normaly ends up in finger pointing and bad tempers and a loss in respect.
I know some companies do have differing ways around it, but most of them seem to be not that successful. Though this is gettin away from the issue of seniority lists somewhat.