As far as I am aware, this is just straight up is not true. Do you have a source for this? Because if the financial sector in the UK halved and moved into the Netherlands and Germany the UK would be doing much, much worse, and Germany much better economically.

See:

https://www.euronews.com/business/2024/01/31/brexit-four-yea...

which is a source that is not going to be biased towards Brexit success, and instead against it (not that there was any success in it, but still).