I wasn't making that point - although perhaps others were. You can't say its a landslide for one electorate and not another - Khan's electorate is London not the country so its an irrelevant point. He won a "landslide" in London if you want to use the 2019 GE figures as a base. Obviously there are different electoral systems at play (Tory wouldn't have a landslide on 42.4% under some form of proportional representation). The Mayor of London has always been "character" focussed, and whilst I might not like it, that's been part of the role.
https://www.london.gov.uk/about-us/mayor-london/mayor-and-his-team/role-mayor-london. He's got a £17bn budget, the vast majority of which is transport; as I mentioned above, that's what gets headlines "Routemasters, "Boris Bikes" (procured under Ken Livingstone!), growth of the Overground, Crossrail etc. The role has a duty to London so when Khan keeps banging on about the "impact of X on London", its hardly suprising... London also has 73 constituencies, more than the entirety of Scotland.
Whilst I agree it's populist and short-termist, other parties had also mooted a fares freeze.
Politics has ultimately moved a lot more that way these decades, I agree its a shame but I don't think its isolated to just London although its probably one of the most recognisable. There's also been this terrible political football of TfL during the pandemic between Labour London & Conservative Westminster which is doing nobody any favours. Grayling also had his spats with Khan regarding rail devolution.