Let me put another fork, knive or whatever in....
Apart from a very few DEC's (at the beggining), the majority are nice guys, competent enough operators, but of a lower standard than the average incumbent FO. I'd like to think they are all "safe" in their role, but they weren't the best choice. It was a marriage of convenience and don't kid yourself that it was anything else. Nothing personal, just stating the facts.
If you are a DEC, either old/new/about to join, then disprove the theory and do the spade work. Read your manuals like the FO's do, study your line training sectors, ask for advice (scary) and demonstrate some humility. You will be suprised at what effect it has. Goodness knows, you may even learn something.
I too have heard the line "Don't need to know that, the FO will have the answers" . No wonder so few DEC's have earnt true respect at Emirates.
Yes, one day I too may take a DEC job. But I will be working my fanny off to make sure I earn (not demand) respect.