Alright, being slightly more cogent now that I've had a minute to breathe. This isn't really positive evidence against the claim that "HPMOR has terrible, nonsensical worldbuidling."
First of all, you've not actually explained why you think that, just made a pronouncement.
Secondly, I don't know why you are participating in a discussion about HPMOR worldbuilding in general, when you've not read the story. Do I really have to respond to your immediate kneejerk reaction about a worldbuilding element you just got randomly informed about?
Seriously, why are you bothering to discuss HPMOR or even worse to pass judgment upon it, if you've not read it? Shall I start passing judgment on things you like that I've not read? Please list a couple such things, so I can bash them from their summaries, without having read them.
Third, I think it actually works MUCH BETTER than the original HP books, where there's all sorts of artifacts (Philosopher's stone, the mirror of Erised, Deathly Hallows, Goblet of Fire, etc) and we're never told why they can't be recreated (though supposedly wizarding technology progresses every year).
In sort the original HP never explain why there's such things as artifact in the first place, things that were created long long ago (like the Invisibility Cloak or the Elder Wand) and that are more powerful than the new ones. HPMOR provides an explanation with the Interdict of Merlin, which causes knowledge of powerful magic to get lost, because it can't get written down.
Fourth, there's also other things it accomplishes (e.g. gives an elegant explanation for Slytherin's Serpent in the Chamber of Secrets: it was designed to transmit Slytherin's knowledge and thus to circumvent Merlin's interdict).