There are very few airlines that employ expatriates that don't have a DEC system, especially in the Middle East, although it is common practice in any rapidly expanding airline, even in Europe and Australia. Only a few airlines, like long established national carriers, are able to offer a protected seniority system, you may not like it but if you plan to stay out in the expat. world you will make life a lot easier for yourself if you get used to it. If you try and give DECs a hard time you will certainly make life very hard for yourself.
In this instance I believe that it is you that is out of step and everyone else that is in step. I agree that in a perfect world there would be no need for DEC. I too 'suffered' from them many years ago and then due to circumstances I had no control over eventually became one. Aviation is no different to any other industry, you sell your product to the highest bidder if you are working as an expat and the better your product the better the deal. I don't think honour comes into it as much as plain old family economics!
You may feel that you have been mislead and badly treated by your employer but there is nothing new to that anywhere and the quicker you drop it as an issue and get on with enjoying life the quicker the time will pass until you are in the LHS. If you dwell on it then it will eat you away like an acid or a cancer and quite possibly ruin your chances of a command.
Just a thought, when you have achieved the LHS and got some useful command time under your belt are you going to stay where you are until pension time or will you then go off looking for a job elsewhere? And if you do leave will you be looking for a job as a captain or as an F/O?