> I imagine in Europe, it's probably Paris and London that draws both French/British and foreigners.

It's not as true in the UK. The salary differential between a medium city and The City isn't as big so while there's definitely more opportunity and higher pay in London it's wiped out by higher costs of living. Lots of people still move there because they like the lifestyle or to climb the ladder faster but if you're content to be a solid well paid professional there are lots of smaller (but not necessarily small) cities with plenty of opportunity, better work life balance and affordable housing.