Also, if you upload a video to YouTube you can download it from YouTube Studio at any time, so that doesn't add up at all.
YouTube just doesn't make this available via API, but you've always been able to manually from YouTube Studio download your uploaded videos.
That sounds brutal if you have 5 years of daily uploads or something like that. At some point, if you want your entire catalog, that becomes a very sucky process.
Just use Google Takeout. It will create a series of archive files for you to download.
Surely you would have the originals locally and not rely on youtube to archive yours uploads?
People who do this are a minority. The vast majority have the masters only available on YouTube.
I hope your “surely” was in jest.