> an LLM vs human interacting with websites would be fairly easy to spot since the LLM would be more purposeful - it'd be trying to fulfill a task, while a human may be curious, distracted by ads, put off by slow response times, etc, etc.

Even before modern LLMs, some scrape-detectors would look for instant clicks, no random mouse moves, etc., and some scrapers would incorporate random delays, random mouse movements, etc.