Who are you talking about? The entire claim was "there was no reasonable description for hypotenuse length before the theorem"; I assume the Pythagorean theorem is intended. But that claim is crazy. You just contradicted it yourself.

I should note that hypotenuses look no different in 126 dimensions than they do in 2 - three points determine a plane, regardless of how big the space containing the plane might be - but that's not really relevant to anything here.