I completely disagree with your conclusion. Videos on YouTube include hours-long presentations of e.g. vortex mathematics which is basically required to view multiple times in order to best understand it. Using bandwidth downloading it multiple times (e.g., streaming) seems wasteful.

Downloading it a single time and watching it multiple times, at one's leisure, whether the website is up, or whether one's even connected to the internet, is a valid use case. Also using VLC you can control the speed with the "[" and "]" keys.

And, as I'm recovering from multiple concussions, I tend to forget most of what I've seen or read. So, being able to download videos so I can watch them again, and sort them into folders so as to assist in my recall, is urgently necessary (and hopefully won't be, at some point in the future).