This is correct. Good rules can't fix a bad GM, but good rules provide clarity and provide tools to better GMs.
A GM who "abuses his authority"--a vague phrase, but I think
@Chaosmancer is coming at it from the angle of "disempowering the players," or perhaps more bluntly, "screwing the players"--is distinct from poor GMing in my mind. A poor GM has problems with pacing, rules knowledge, engaging with the table, punctuality, or otherwise has habits that result in a lesser gaming experience. A GM who "abuses his authority" cannot be resolved with rules because he's not going to play by the rules anyway. He's going to run roughshod over the players whether or not the rules tell him he can or cannot do something.