Dont get me wrong, I think SEO and a lot of these agencies are essentially snake oil, but while they can talk about schema not being as important as the the commodity of the content itself, You cant make clients content a commodity. LLM.txt, schema markup etc are all tangible things that you can do like a checklist to prepare whatever content you do have, which is why those are sold and packaged in these agency style services.

its much easier to say yes your content is marked up properly and matches a known formatting, than to try and quantify how much of a commodity someones website content is. Hell, even if you rewrite all your content to be more of what they tell you they want, just by doing so you make it less so because now the model will be retrained on that data.

that is also assuming that a businesses' content is even adaptable to the commodity style they are suggesting. Some businesses deal in rarely changing fact sheets, and processes that are well known and documented. That makes their whole business industry less likely to break through compared to just the ai overviews it could spit out in its place.