So the questions I'd ask are: How far spread is this manipulation, does it work for non-niche topics and who's benefiting from it.

Very, yes, and pretty much anyone that doesn't want to spend their days implementing counter-meaeurements to shut down their scrapers by hiding the content behind a login. I do it all the time, it's fun.

I'm gonna single out Grokipedia as something deterministic enough to be able to easily prove it. I can easily point to sentences there (some about broad-ish topics) that are straight up Markov chain quality versions of sentences I've written. I can make it say anything I want to say or I can waste my time trying to fight their traffic "from Singapore" (Grok is the only "mainstream" LLM that refuses to identify itself via a user agent). Not really a tough choice if you ask me.