Ah, OK, then I don't understand how you came to conclusions about bad GMs "while I was the full-time GM for my group". How did you come to conclusions about other bad DMs (I suppose it's about others, not about you) while being a DM yourself ?
Yes, you did, because I said "to give full reins to the players in terms of actions and description", for once, and second, nowhere in the rules of the game does it say that the players have full rein about anything, including actions. If they ask to do something that is physically impossible in the game world (for example fitting through a hole that is too small for them), they have zero authority if the DM tells them "your character cannot do that".
At our tables, in general, the players and the DM are sufficiently in line so that there is no disagreement about what a character can do, but in case of discrepancy, it's solved through simple clarification as well as mutual respect and trust, that's all. There is no need to assert any authority, the players know that the DM is in charge of the world anyway, but that if he decides that something in the world is a certain way (the hole is too small), then it's certainly for the best in terms of story, and no one argues.