You could say ATP wannabees is a slur too if you're really trying to see an argument where none exists. Wheelchair tennis is fine and has its place. It ought not to displace other aspects of tennis (which ultimately are arguably more important) or be used as a figleaf. As you point out yourself, the NTC is a badly utilised resource.
"The NTC provides a world-class facility for young players, international wheelchair players and the administrative headquarters . . . "
Tennis is a game for life for everyone. That's the fundamental, hence inclusion of wheelchair tennis i.e. a game for everybody, all ages all abilities. But there's a massive gap between young players and international wheelchairs players some of whom wouldn't be British anyway. The NTC excludes those and that's the point. When it comes to it, they aren't that inclusive. And aren't that British.