At least in the U.K. it's entertainment industry is mostly decentralised and located away from London, more in Wales, N. Ireland and Milton Keynes.
and Nagoya is Japan's Detroit if Detroit hadn't become Detroit.
Sort of. Toyota and its suppliers are there, but Honda, Nissan, and Mazda are not. Detroit was unique because it was the home of every major American car company: Ford, GM, Dodge/Chrysler, and AMC.
The GDP of the Tokyo metropolitan area is about 1/3 of Japan's total GDP. The country is weighted toward Tokyo like the UK is weighted toward London.
In the US, the center of finance is New York, the center of entertainment is LA, and the center of tech is Silicon Valley. In Japan, Tokyo is the center of all of those things, as London is in the UK.