> Browsers don't bypass the protection mechanism, they implement it.
This is incorrect. The website implements the protection mechanism, browsers execute it, just as youtube-dl. The implementor is the person writing the code, not the system executing it.
> Certain YouTube videos are licensed only for streaming playback by the YouTube site or app.
The meaning of this sentence is unclear. What does it mean for playback to only be allowed by the (web)site? Websites alone cannot do anything -- they require a web agent which fetches and executes them. Firefox, Chrome, Safari and youtube-dl are examples of such agents.
> Even if this were not the case, you would be committing copyright infringement by downloading the videos for unauthorized use anyway.
Luckily for me, I am in a jurisdiction where this is not the case and where DMCA plays no role.