As someone who joined a 'good' company where the seniority system was usually fairly administered I had no gripe in waiting my turn for promotion/type progression. My more senior colleagues used to remind me that eventually I'd get to the top of the list, just like they had. All it took was patience.
Then about five years ago the new management began bending the rules, then they stretched them, then they blatantly broke them wide open. As a result, pilots who were still in short trousers when I started flying jets, were promoted over my head because it suited the companies selfish needs. It had nothing to do with ability...because it was done to a whole group of contemporaries of mine. We just happened to be on the 'wrong type' at the time and the company saw the opportunity to save money on type conversions by promoting junior F/O's from right to left seat. As a result of this outrageous abuse my carreer was damaged permanently...a freeze system operates in the company and I was forced to make bids onto types that I should have naturally been directed onto (with no resultant freeze). Also, the two years more I spent on the 'old' type was a penalisation that I get no future credit for...so I'm two years set back in my carreer development.
One other thing got broken that day. It was the faith and loyalty I had held in my company and its management. I also lost a lot of respect for my union, which let it happen, and the colleagues who took advantage of the opportunity to screw me and my contemporaries for their own personal gain. It hasn't been forgotten. I'm loyal to one thing now. Me.
The point of this whole rant is that anyone who thinks your experience level (as a measure of merit) has any real bearing on a company making crew appointments...you're naiive in the extreme. Only one thing matters, and that's money. The bottom line. If there is no restriction (i.e. no seniority system) then they'll hire, fire, and promote or upgrade solely according to fiscal necessities.
So I guess I agree with those who said seniority is a pain in the arse, but it's better than the alternative.
Thank you for giving me the opportunity to get that off my chest.