Seniority to bid for domicile is not unique to aviation. Here in Australia, a new teacher working for a government education system is likely to get posted to some little hick town initially and only work back to a more desirable metropolitan post after serving time in the bush. Ditto for cops, air traffic controllers, nurses, priests etc.
The old bid system for flying patterns and leave was a bit unfair, because as has been mentioned, some guys might have to wait many years to get the decent trips or Xmas leave. It is preferable to share that equally i.e. if you get Xmas this year you go to the bottom of the waiting list next year and work back up until it's your turn again etc.
As for equipment assignments - why shouldn't the longest serving (and hence well-known and probably more likely to stay) pilots get first crack at the bigger or newer gear? If I had been with an airline for 10 years, always performed well, done a good job etc., and a new wonderjet was introduced I would be mightily disgruntled if it was fully-crewed by DECs or two year tyros. Airline managements need to balance the financial disadvantages of seniority against the benefits of lower crew turnover.
And for those who argue seniority stifles mobility, with sufficient experience under your belt there are always opportunities elsewhere to start again without losing captain rank. Just not in your home-town with your legacy carrier. If you missed out there or chose a different path when you could have had a job there, you can't expect to swan in now at the top of the tree. If being at home is now your priority, accept that you WILL start at the bottom again.