The end game of that is no useful content being accessible without login, or needing some sort of other proof-of-legitimacy.

That's already the case (irrespective of residential proxies) because content only serves as bait for someone to hand over personal information (during signup/login) and then engage with ads.

Proxies actually help with that by facilitating mass account registration and scraping of the content without wasting a human's time "engaging" with ads.

Amazon.com now only shows you a few reviews. To see the rest you must login. Social media websites have long gated the carrots behind a login. Anandtech just took their ball and went home by going offline.