I have GMS as well as C2 and I would be very interested to see the files you used for comparison.
Just from little testing I've done, I found I can create the GMS demos in C2 in a ridiculously short time, whereas anything of note in GMS needs to be done in GML.
But, as everyone else has noted, to get the best out of either - or any software really - takes time, effort and a lot of practice.
If you're getting disheartened, then do small prototypes of the problems and post them for others to possibly help.
Never hurts to ask for help.