Such claims have always been made about seniority-based employment systems, i.e. "Yes, advancement on merit is all very well for lesser callings, but we are special, and must maintain our current system".
Pilot advancement is entirely on merit. It is called the Command Check.
A Seniority list merely determines
who's turn it is to demonstrate their aptitude.
I am not aware of any circumstances where those claims have ever been proven accurate.
Really?
I see it proven every day.
But there are always strong vested interests in maintaining the status quo, the natural conservative instincts of professionals such as pilots work to resist change, and (perceived) self-interest kicks in once a moderate amount of progress up the list has been achieved.
Yes. Those without the Seniority think the system stinks.
Then they get some seniority.
Still. Advancement on merit will come to pilots eventually - perhaps even be forced upon them, as with so many changes, in response to external pressures - and will probably quickly come to be seen as having been long overdue.
It's already here. Many pilots live with it.
They are no more happy, I can assure you.