There are many totally different parts to London. I often spend time in the suburbs- there are streets and streets of lovely houses from maybe 1930s nd some more modern ones- interspersed with lots of parks and small woodlands. Richmond, Enfield, too many to mention. The centre of London is not a rat hole and the foreigners that 'infest ' it are Europeans, Americans , Aussies and Japanese/Cjhinese- but overall I was struck by how 'white' the city was- very few Muslim looking types. But then ge on the tube and the ethnic mix is clearly much more varied. Then go to some of the areas like Hackney, Brent Cross, Whitechapel etc and you see the majority of the population looks of non-white heritage and there signs of poverty mixed with flashy BMWs driven by 19 year olds. Even Kensington has multi million pound homes and Grenfell Tower.
Overall, London is no rat hole, but there are some parts I would not choose to live or even visit