Everything is nuanced and generalizations help no one. There are absolutely frontend apps where AI straight up crushes. Sure these much be less novel apps but most of what people work on is a CRUD-esque interface.
The author of the post is known for some pretty fancy CSS wizardry. I’m guessing AI is not great on some very specific, advanced CSS use cases where there isn’t much prior work. But again this is an edge case compared to what the vast majority of us are doing