The key to being a good GM or anything else is to be a good counselor and be able to make a compelling case to the boss to convince the boss of your position. If you are very effective, you can get the boss to agree with you and think it was their idea. That is what I tried to do in my career as a counselor. I had no authority to make the decision so I had to help lead the boss to the right decision. If GMs are getting overruled by their bosses on a consistent basis, they are not good at their jobs. If they have the data, research and expertise, and good communication skills, they should be able to get the boss to buy into their plan.