Pool you are right of course, DECs join knowing the same about EK as FOs do, so why should they complain when the rules change eh? But I wonder how you would react if the company turned around to you and said.."sorry old chap, we have an FO ready for command who has a higher company seniority to you. I'm afraid you were the last DEC to join so you will have to become an FO so he can have your left seat" You wouldn't get on Pprune and whinge about that would you....?
Funny how you start a post complaining about DEC bashing, knowing full well that the post will only lead to more...