So here is my input.
I'm nearer retiring that starting my career. I've done military, civil, long haul, short haul, national airline, charter, major low cost, wide body, narrow body, airbus, boeing including management time and training roles.
The truth is that there are good and bad guys in all areas. Todays long haul captain is tomorrows low cost captain and it works both ways.
There is a certain arrogance in SOME posts here from EK that SOME there think they are better than others. It is quite correct that if recruiting DEC's there should be a high rejection rate at selection; if that high rate continues during training then there is either something wrong with the training or there was something wrong with the selection.
DEC's bring different experiences which can be useful and amongst other things, can help to avoid those within a large company thinking that they are in some way superior - they probably are not. A DEC will inevitably take a little while to become familiar with new destinations but this is not unsafe; if it was how would any airline ever go somewhere new?
A large company like EK can absorb some DEC's and benefit from the experience whilst still leaving the large majority of LHS slots for internal upgrades.
Finally, few of us these days join an outfit as a young F/O and stay there until we retire. Most will at some point leave, quite possibly from the LHS and seek a DEC job somewhere so just cut the hypocritical rubbish.