I worked a little with Mayer at Google. She was reasonably intelligent, but she’s one of these people who believes that being decisive and certain and barking out orders trumps honest uncertainty, suspending judgement until you have all the facts, and a sense of humor.
This sort of strategy only worked IMHO because Google had a flood of incoming money so anything you touched would turn to gold.
I saw no depth or competence in her, and it was zero surprise when Yahoo failed, although I was still surprised how truly badly she did, and how badly she treated her workers (but then Google goes out of its way to treat you well).
I want to add that these characteristics were not typical of the rest of Google senior management, who generally were a decent, intelligent group quite open to ambiguity or the possibility they were just wrong.