You're not looney at all. Frontier models do dumb things all the time, especially on mature codebases. Just yesterday Opus 5.5 butchered the OOP model in a codebase I work on - it duplicated a load of classes that should have just been subclasses. A junior checked it in very satisfied that it was perfect. The LLM review passed it, the tests were fine, and it implemented the feature successfully. It's just the code design had poor taste and poor long-term maintainability.

I keep seeing this kind of thing over and over, and honestly it's not got _that_ much better since the big breakthroughs about a year ago.

For sure I happily vibecode stuff without worrying about it when it's a greenfield project, and if the LLM has written it entirely from scratch then usually it's well structured and sane. But making changes in messy, mostly human-written mature codebases is still a minefield.