I never want work for an airline where the chief pilot decides who gets promoted this week. Seniority is like democracy - it is full of flaws, but a million times better than the alternatives.
Exactly.
The seniority system does work on merit btw - when your time for command comes you'll be rigourously assessed. If you meet the high standards required then you get a command. If you don't, you don't.
The training department ensures that only people who meet the required standard get commands. The seniority system ensures that meeting the required (high) standard is the only criteria used, not whether you play golf with the chief pilot.
The system is completely fair and has existed for decades and everyone knows about it. If you choose to pursue other career options before joining a 'seniority airline' then that's fine, I hope you enjoyed it. But don't now bitch about a perfectly fair system, that many made sacrifices to join earlier in their career.
As has been said by many, the airlines with the best Ts&Cs seem to be the seniority based ones.