It’s somewhat of a catch, that’s generally how monopolistic moats work but you really shouldn’t be relying on google as a backup service for obscure videos you wish to keep.
I’ve no idea of the amount of lectures, guides, documentaries and other non-entertainment media that is available exclusively on youtube, but again it isn’t an archiving service.
They can, will and have deleted whole channels for various reasons, most of which were bullshit, if you find something you absolutely have to keep, download it.
That being said, the process of downloading, archiving and curating content on anything more than a trivial scale can be much more involved than it seems, especially if you want backups/redundancy.
I’ve never been a big youtube user so my opinion on this is coloured by the fact that i don’t have that much invested in the platform.
Not sure how versed/willing you are to selfhost but I’ve heard good things about tube archivist.
There are also a bunch of ui’s for yt-dlp, though i can’t vouch for quality.