You are quite right that there is (and always will be) a great concentration of wealth in the capital, and that it's an international centre of the Arts, and has been for hundreds of years (if not more); both those facts are undisputable.
But have you been to London recently? The poor areas continue to deteriorate, the problems of crime, drugs and lawlessness are near breaking-point, imho. Many areas are approaching third-world in terms of services and the danger on the streets. We have floods of poor immigrants (both legal and illegal), many hundreds of thousands every year, who put a strain on the resources that will have repercussions for many years to come (and btw, I in no way blame those immigrants, but the sytem and the government who enact failed policies, and don't even properly put into practice the ones they have at their disposal which might work.)