Couldn't the original website owner just look at the logs and see where most of the requests are coming from? And also the referrers would be a dead giveaway, right? That's assuming someone is looking at the `access.log` file occasionally.
They could use residential proxies
And residential proxies are becoming increasingly legitimate because of over-zealous AI blocks.
Blocking IP ranges and user agents has nothing to do with "AI". It's a bad practice by lazy sysadmins who'd rather discriminate users than fix their infra. Writing this from a non-profit ISP (fdn.fr) whose IP range is blocked by Google and Reddit and noone still knows why or how to unblock it [0].
Residential proxies on the other hand i don't think have any legitime usecase. I would support people working around Youtube to export interesting videos to Bittorrent. But what's happening is malicious actors going around rate limiting to run bad-behaving scrapers on smaller sites. That, and much worse is the residential proxy economy.
[0] https://www.fdn.fr/the-fdn-and-gitoyen-networks-are-blocked-...