I'd say the UK is too centralistic. Back when my field of work included "media" it was said that every company with a foothold in the UK needed to be in London, anything else wasn't so important. I think it's a bit the same in France - be in Paris or be bust.
Take Germany as a contrast. If you exclude weird fringe stuff (not on this site, you should get my point) like startups - it's all over the place. Sure, the banks are in Frankfurt - but the media stuff is pretty much divided between Hamburg, Munich, Berlin, Cologne, Stuttgart. Also all the "big" well-known companies have their headquarters either in any big, or even a small city. That's why the rent in Munich is quite high, but nothing compared to London - and Berlin is quite cheaper.
I wouldn't say it is a problem on its own. Look at Japan. Almost everything being in Tokyo is not a problem because their transport system is excellent.
The UK's problem is that transport policy is abysmally backward and our property market is outrageously disparate and historically overvalued (as land was how a person demonstrated their wealth which has perpetuated unlike other countries where industry holdings are valued much more, e.g. America and Germany). Take your example of Paris, much smaller but equally historic, yet prices there are much lower than in London. London is a more global city than Paris but not so much as to explain the discrepancy in property market values.
