The crime rates in other places is irrelevant if the city you've lived in for the last 20 years has become noticeably more dangerous.
This is not "a narrative that keeps being pushed without merit", in fact the people who dismiss such claims are often the ones who live very insulated lives.
Brexit has markedly made the UK's economy weaker, there are less opportunities, the opportunities that exist outside of finance/tech are quite low paid compared to other European countries while the cost of living in London is absurdly high when compared to other major European cities. It's the perfect storm coupled with high immigration: blame immigrants for the lack of opportunities caused by a policy pushed by anti-immigration rhetoric, it will just feed into giving power to Reform which, if given power, will continue to crash the UK's economical prospects.
The ship has sailed, it will take the UK quite a while to correct course, perhaps even a generation or so... While that correction course happens British society will just keep eroding away.