I'll tell you what. Have a look at the industrial strategy outlined by the government. Clusters such as life sciences and artificial intelligence are generally focused around world class universities, which are all located in cities. I know you don't like that fact and think we can thrive by returning to an agrarian society, but it's not really in keeping with reality.
"Cardiff has an ethnically diverse population due to its past trading connections, post-war immigration and the large numbers of foreign students who attend university in the city."
https://en.wikipedia.org/wiki/Demography_of_Cardiff#Nationality
Granted, it's not London levels, but it is by far the most diverse area in Wales and followed the trend of most of the UK, of areas with most diversity voting remain, and those with least diversity voting leave.