Not a single bit of evidence has been given, even circumstantially, that actually supports generic water changes at a specific interval.
What we have is people arguing that conditions can exist that MIGHT call for water changes. Nobody ever denied that. But there's no reason to think that doing one every day or week, just because an amount of time has passed, is necessary.
The best anyone has proposed is that it's easier, for those who cannot be bothered with anything more complicated. And that's fine, but such people shouldn't go around telling other people that you MUST change ANY tank's water every N interval.
This is a case where you who claim otherwise must offer the proof. You are making the positive claim. Skeptics need not prove anything but that you have not given that solid proof.
If you were saying that a banana must be floated in any tank containing charicins, it would not be up to your opponents to prove that it is not necessary, but you to prove that it is. That is also the case, here.