7Q, I didn't say that I hate seniority. Please do not tell me what I hate, it makes you look foolish. I have worked in several seniority driven systems. All stuck to seniority rigidly until it didn't suit them. Airlines will bypass seniority when they need to and use it as an excuse for not doing something the next day.
What I said is the concept (in the modern world) is insane. In a different era with cradle to grave jobs it was a valid way to manage progression within a company. Those days are over. Even if you are at the top of the tree in a legacy carrier you would be brave to predict that you could not be the victim of another failed airline. There are many examples.
I agree that the companies that do take DEC's generally do not pay particularly well, however there has been a downward trend in conditions in the industry. A new hire at any legacy carrier that I am familiar with will not be on the same package as his colleagues that joined earlier.
Most normal industries hire a person with a skill set to perform a given job. They may have a preference to promote from within which is great, but they generally will not preclude external applicants from consideration if they have something to offer. It is also unlikely that a person with years of experience will go from a senior position to an entry level position just because they change company (unless you are a Pilot). If they are unfortunate enough to find themselves out of a job they may have to take a job that is not quite at the same level but they do not end up in a trainee or new graduate position again.
In some cases seniority does not even protect you as the ship sinks. The concept of "last on first off" no longer stands up industrially (in some countries) as companies argue successfully for targeted retrenchments on particular fleets or bases.
So is there a place for seniority in the modern airline world? Well if you work for a well managed and profitable company that will probably outlast you, well maybe but they are few and far between these days.