[Citations needed] or it didn’t happen.

I think this mindset is naïve and unrealistic.

People were saying the same thing for decades in response to a small minority warning about government surveillance, often dismissing them with labels like "paranoid". Eventually, Snowden came along and produced the citations, at extreme risk to himself and his loved ones. It's an anomaly that they were ever revealed at all.

History is replete with examples of bad stuff going on for ages before irrefutable evidence of it became widely known. In general, if something can be abused to someone's advantage, it will be, and likely already is.

There’s precious little extra information that a “nefarious” instance can harvest that any basic web scrapper can’t.

You have a point there, but consider also that effective web scraping uses significantly more resources than having the data you want handed to you. Monitoring Lemmy through federation would be much more efficient.