I think one of the issues is that we live in a part-seniority, part-not world. Those who want to move out of a seniority-based airline lose the advantage of the years they’ve put in and those who want to move in can only join at the bottom as an FO. With incremental pay scales this can be a real killer in both directions. At the same time, how do you reward loyalty?
It also very much depends on the gradient between top and bottom: if you’re all paid much the same and do roughly the same amount of work, then absolute seniority isn’t such a downer. There are ways of giving most a bite of the cherry without having to spend their whole working life with one employer.