Travel time by train is mostly about how many stops [edit: legs] you need (which add through wait times) and what part of the network you're on: Brussels/Cologne, which is used on the London/Cologne route was only usable up to 60km/h or so 7 years ago. That part took nearly as long back then as the entire LON/CGN trip does now.

Paris - Stuttgart - Nuremberg (580km) takes 6h51 including one hour between connections in Stuttgart.

Berlin - Stuttgart (591km) has a 5h34 direct connection.

Frankfurt - Bern - Milano (~700km) takes 7h47 including 30 minutes in Bern

OTOH, Frankfurt - Cologne (for which a dedicated high speed rail route was built nearly 20 years ago) is about 200km in 1h04.