I’m not sure I’ve ever had anyone seriously suggest that one area of the country is “better” for mountain biking, perhaps as a joke or in passing…
Of course as we all know the East Anglia area is shite, simply too flat and dull, but just about everywhere else has some hills, and thus some reasonable riding….
I’m sure there’s some grizzled old Yorkshire men who simply despise the south and all it stands for likewise some Cornish fella who can’t stand all the northern monkeys, personally I find I get on with most people regardless of their regional origins…
Most of the country can unite in it’s hatred of Londoners though; mostly useless gits hoovering up resources, Bumping up the cost of housing, generally achieving nothing but doing so in the most costly and “fashionable” way possible… But London isn't the "Proper" south anyway…