I might as well contribute to the thread drift.....
That is exactly what happens. When your time comes, you do your command course and are "Promoted on skills and merit,"
How else would you determine a person was ready for his command course if you do not use seniority? Best at brown nosing management?
There is no indication of mischief-making in the post so I'm assuming it's intended in all seriousness.
First, a disclaimer, I'm not a pilot - just a simple controller. We don't work in 'crews' but we do have supervisors.
I have worked with some excellent supervisors, and more average to appalling supervisors. The less able individuals were, without exception, given the job on the basis of seniority - they were next in line. In these more enlightened days (in some parts anyway) supervisors are generally selected on the basis of their knowledge, skills and potential. One of the best supervisors I ever worked with was a young 'un (I'm now old enough to look around me and see many "youngsters") who had relatively little operational experience and did not particularly distinguish himself as an operational controller but did all the supervisory stuff superbly.
Now I'm not trying to say that the role of aircraft commander and ATC supervisor are the same but there undoubtedly some comparable elements. But I am trying to say that seniority systems based on years in service do not necessarily produce the best results and can be rather easily abused for unrelated reasons.