But the main point of this is that it's not up to the Mayor if he's "had enough". The Commissioner of the Met manages more than just London policing, so hiring and firing them is for the Home Secretary. The Mayor gets some input into appointments, but to suggest the Commissioner has to go if the Mayor is unhappy is an overreach of his powers.As Winsor had on a number of occasions, including some at a very late stage, expressed support for Dick, he is hardly likely to be, or at least be seen to be, a totally impartial investigator. However, that is on Patel’s account as she chose him. The Mayor is supposed to hold the Commissioner to account and if s/he fails to deliver an adequate programme to deal with problems, it is not unreasonable for the Mayor to demand a revised and improved programme. If the Commissioner fails to provide such a revised programmme and does not even attend the meeting with the Mayor to explain, it is hardly surprising if the Mayor finally decides that they have had enough. Particularly if the Commissioner seems to be in denial about how serious the problems are and the resultant widespread loss of confidence in the Met.
Note: I don’t live in London and have only followed the story casually, so the above is my opinion, particularly the last sentence.
As you've said this is your opinion of the events. I would suggest another interpretation from reading the report is the the Commissioner did submit a plan a week earlier to which the Mayor failed to respond to, but instead made public statements about his loss of confidence. If your boss stopped talking to you, but instead went around badmouthing you, wouldn't you be reluctant to go to a meeting with them?