Yes a lot of instructors feel shafted, but consider this also. If you feel you are being shafted, what did you agree to when you first started working there? If you agree to work for peanuts and wash the boss's car and executive washroom, then you can't then turn around and say that you are being shafted when you are asked to do exactly that.
When I started up I only ever gave new instructors the realistic view that I would provide an infrastructure within which they could develop their careers if they provided their own students initially, but the rest of the work would be done by myself or my senior instructors. Yet still I had accusations of "you never give me any students!"
I will add that my instructors don't have to be there unless they are flying, and the front desk is done by full time ground staff, the instructors are never asked to do anything but instruct.
I know there are employers who expect you to be there all day, and pay you only for flying time. No, this is not good, but if you agreed to it then you have created the situation yourself. The thinking that if you didn't take the job someone else would is not necessarily so, we all started somewhere, and when you reallise that success or failure is your choice and not your employer's, then you too will succeed.
Good luck!