Cloudfare have a clear advantage in the sense that can put the door away from the host and can redistribute the attacks between thousands of servers. Also it's able to analyze attacks from their position of being able to see half the internet so they can develop and implement very efficient block lists.

I'm the first one who is not fan of cloudfare though. So I use crowdsec which builds community blocklists based on user statistics.

PoW as a bot detection is not new. It has been around for ages, but it has never been popular because there have always been better ways to achieve the same or even better results. Captcha may be more user intrusive, but it can actually deflect bots completely (even the best AI could be unable to solve a well made captcha), while PoW only introduces a energy penalty expecting to act as deterrent.

My bet is that invidious is under constant Google attack by obvious reasons. It's a hard situation to be overall. It's true that they are a very particular usercase, with both a lot of users and bots interested in their content, a very resource heavy content, and also the target of one of the biggest corporations of the world. I suppose Anubis could act as mitigation there, at the cost of being less user friendly. And if youtube goes a do the same it would really made for a shitty experience.