You're right GF is not BA or AC etc. But firstly let me start by saying the list of cariers flying the Ejets is growing everyday, and I know for a fact that there is a demand for Ejet pilots not a surplus.
As for working conditions and having leave cancelled its the same in QR so again, not something new. Pilots all over the GCC are complaining about working hours.
Yes, if you simply want to come to GF to advance in your career and to use it as a stepping stone to somewhere else, which I am assuming you do, then moving to an Regional jet probably isn't the best career move, especially if you want to be flying wide body jets within the next 5 years or so.
The reality is that GF have 4 Regional Jets and should have around 20 airbus narrow bodies by the end of the year. So the chances of you being upgraded to captain on an RJ is slim. I know of a few 330 FOs that are being upgraded to Captains directly on the 330.
Yes it is true that GFs promotions are not always honest and people are looked over for someone else because of wasta, so you might be stuck on these planes longer than you might be if the system was honest, but you are still getting paid well and its not something that you don't see happening in QR or in EY, not sure about EK, I hear they have their house pretty much in order.
I hope you realize that QR and EY are pretty much being run by Ex-GF folk.