Of course it's meaningful. Because, due to its size, the Pearl River Delta contains what are essentially 11 different cities - each with its own city center. Where as the Greater Tokyo Area includes 6 - all substantially smaller than, and largely centered around, Tokyo.

Speaking about your other attributes... I think the most telling thing about the Pearl River Delta is that 2 of those 11 cities were governed by the UK until 1997 - and you still have to pass through customs and immigration to cross into and out of them...