Yeah JKR is just immensely bad at world building and macro level details - how, in the hundreds or however many years the Triwizard Tournament has been going on, has no one thought to enter someone else's name? Why didn't any of the spells on the cup detect that sort of fraudulent entry, but it could detect magic that physically ages a person? Those kinds of logical holes and inconsistencies are everywhere in her writing. The thing she usually gets right though are the micro details - she's decently good at character building, character interaction, and keeping characters true to their… Well, character, throughout the books.