CUPOFTEA, I like your reasoning but, I think your argument fails when you start comparing the career structure of medicine with that of aviation. Aviation is almost unique in the way that the career structure is limited by the size of the workforce, the limited number of respectable employers and the (almost) sole opportunity for promotion from r to L seat. Medicine has a much wider choice for people to move up or sideways due to the huge numbers of doctors employed in a given country compared to employed pilots. It is a much free-er market than we have in aviation.
Respectable airlines tend to steer clear of DEC's unless the need is dire. The reason is simple. There will almost always be an ample supply of tried tested and graded Fo's waiting for upgrade. Sure in boomtimes there can be a shortage of people of the correct calibre, but that has usually gone hand in hand with a rapid growth of the business and quickly dis-appears when growth flattens out. When did you last see BA looking for DEC's? Almost never.
Then look at the available DEC's, they are either the pilots who find themselves in the unlucky position of redundancy and there are those who might struggle to pass a decent interview. Those pilots that thrive on the excitement of contract work, won't be looking for a DEC job normally. So, for the employer, there is still no advantage in the DEC who has trained to different SOP's, not got an in-house training record and may have an 'unfortunate history'. Added to that is the bad feeling that DEC's can create within the company, not great for CRM.
Seniority has been threatened before and is still here, admittedly with modifications, and works well for the unique airline model. All the airlines that I observe without seniority have, in part, unstable workforces, low morale, low pay, poor conditions, high staff turnover, little loyalty and I don't envy anyone working for one.
We have had several years of new pilots and unscrupulous employers lowering the t&c's for everyone else worldwide, probably time to stop it now.