The thing about this whole post is that AI-written text doesn't tell you a single thing about whether a human was involved.

A thing about tier 1 CS agents is that they are often not highly literate and great at writing, and companies go to great lengths to minimize how much text they need to freehand, with tons of pre-writes to address common situations. LLMs allow the agent to express some freeform idea and have the LLM clean it up to read clearly and professionally. So even if you are 100% dealing with a human, you should expect nearly all text from them to be LLM-written.