Arabesque is not a weak gene that we know of.... I have a 2004 arabesque het albino female that was nearly breeding size at 2 years old. Never refuses a meal and grew like mad. She is now over 7' and 26lbs on empty. I wouldnt worry too much about over feeding your arabesque.
The fact that it is spitting up food, give it a week or 2 without even trying to offer any food. Let it's stomach settle, then try a very small item. I believe you said you were giving hopper mice? Try a smaller hopper, maybe even a fuzzy. Let that item digest completely and slowly work your way up to bigger items over a few weeks/months.
As far as why don't we see supers yet.... thats a good question. It's unknown if a super form of arabesque even exists. Several people have done arab x arab breedings, all of the babies look like normal arabesques without a definitive super form such as the motley gene provides. but I dont know of anybody breeding those offspring to prove it out as a super or not. The common belief as of right now leans more toward the arabesque gene not having a super.
But for your main problem being feeding, once you get your arab started on food without throwing up, i wouldnt worry about how much you are feeding it, feed it like everything else, I always have with my arabs, and have never had a problem.