I think there’s probably already enough information out there to see how pedantic the typical audience is here ;)

"I was only pretending to be stupid!"

D'oh!

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.

If you believe that you can only subtend a 90 degree angle, sure.

("Subtend" is a direct part-for-part translation of the verb which also gives us the name "hypotenuse".)