Sadiq Khan has not been a great mayor for London:
1) He spends much of his time on luxury holidays and not in London
I looked this one up. All I could find were a million whinges, mostly in the Murdoch-owned Sun, that he took a long weekend in Morocco earlier this year
2) He has zero presence and we never see him anywhere, ever.
I see him plenty. For instance, he was on the scene at Grenfell a hell of a lot more quickly and usefully than Theresa May.
3) He has put very little imagination or flair into encouraging business to come to London
What exactly do you think he should have done, particularly given the massive handicap of Brexit-induced uncertainty?
4) He is basically completely invisible unless he is tweeting about Trump
If you think he's invisible, you are closing your eyes to the facts. Johnson attracted more publicity, but he was a lousy mayor and essentially the publicity stunts were a smokescreen.
5) He has done nothing at all to address the serious issues of knife crime, cyclists being killed every day on the roads, pollution or any number of things that are important to our lives every day.
Again, not true. Road deaths in London have in fact fallen to the lowest on record; as for cyclists being killed "every day", last year the total number was 12. As for pollution, we now have the Ultra-Low Emission Zone, money made available for electric car charging points to be radically increased, local low-emission zones and traffic reduction initiatives, steps to make public transport and taxis low or zero emissions capable, low pollution initiatives around schools etc etc. Knife crime is a serious problem, but what magic wand do you suggest Khan waves given the massive budget cuts for the Met and for youth worker initiatives that the government has imposed?
And, before you suggest it, I have no direct or indirect connection whatsoever with Khan. I simply keep my eyes and ears open and read the news.