Where in this post's article are you seeing this pattern?

> Parsing a known HTML structure

In most cases, HTML structures that are being parsed aren't known. If they're known, you control them, and you don't need to parse them in the first place. If they're someone else's, who knows when they'll change, or under what condition they're different.

But really, I don't see the stuff you're talking about happening in prod for non-one-off usecases. I see LLMs used in prod usecases exactly for data where you don't know exactly what its shape will be, and there's an enormous amount of such cases. If the same logic is needed every time, of course you don't have an LLM execute that logic, you have the LLM write a deterministic script.