The argument the article is making is that if they really wanted YouTube downloaders to stop working, they'd switch to Encrypted Media Extensions. Do you think that's not plausible?
Once those devices get phased out, it is very likely they will move to Encrypted Media Extensions or something similar, I believe I saw an issue ticket on yt-dlp's repo indicating they are already experimenting with such, as certain formats are DRM protected. Lookup all the stuff going on with SABR which if I remember right is either related to DRM or what they may use to support DRM.
It's much more likely YouTube just doesn't want to mess with it's caching apparatus unless it really has to. And I think they will eventually, but the numbers just don't quite add up yet.
> If you choose to upload Content, you must not submit to the Service any Content that does not comply with this Agreement (including the YouTube Community Guidelines) or the law. For example, the Content you submit must not include third-party intellectual property (such as copyrighted material) unless you have permission from that party or are otherwise legally entitled to do so. [...]
> By providing Content to the Service, you grant to YouTube a worldwide, non-exclusive, royalty-free, sublicensable and transferable license to use that Content (including to reproduce, distribute, prepare derivative works, display and perform it) in connection with the Service and YouTube's (and its successors' and Affiliates') business, including for the purpose of promoting and redistributing part or all of the Service.
If you include others' work with anything stronger than CC0, that's not a license you can grant. So you'll always be in trouble in principle, regardless of whether or how YouTube decides to exercise that license. In practice, I wouldn't be surprised if the copyright owner could get away with a takedown if they wanted to.
To date, many Creative Commons licenses do in fact amount to "permission from that party", but if they start using DRM, those licenses would cease to grant YouTube permission.
> No downstream restrictions. You may not offer or impose any additional or different terms or conditions on, or apply any Effective Technological Measures to, the Licensed Material if doing so restricts exercise of the Licensed Rights by any recipient of the Licensed Material.
(https://creativecommons.org/licenses/by-sa/4.0/legalcode.en)
Most of the CC licenses include such language and have since the first versions.
Wrong question leads to the wrong answer.
The right one is "how much of the ad revenue would be lost if". For now it's cheaper to spend bazillions on a whack-a-mole.