I would suggest you look into whey they serve content as Webm and why V8p came about initially in the first place. I recommend you watch this lecture if you want to deep dive on the topic and how youtube uses the codec.https://www.youtube.com/watch?v=pFK35DrsFY8
There are a couple lectures on the topic if you want to really learn but this is a good starting point. You really need to understand that economic/speed tradeoffs mean that effectively they aren't ever going to be able to serve content in a way that is both fast, economical, and hard for the enduser to steal/download. These tradeoffs are pretty baked into how most audio/video sites serve content, most optimize for fast and cheap solutions that are easy for technical people to download. I guess they assume that most people won't use something like youtube-dl which is probably a good assumption.
Anyway in my opinion unless you know of some neat new alternatives, content serving solutions at this kind of scale are probably going to follow this model and will thus be easy to download content from.