Your view from a distance, where you rarely download Youtube videos, is common for now, and we still live in a very fortunate time. The problems are short lived, so over long periods, they tend to average out, and you are unlikely to notice them. Even active users will rarely notice a problem, so it is understandable for your use case, it would seem perfect.

Looking closely, at least for yt-dlp, you would see it tries multiple methods to grab available formats, tabulates the working ones, and picks from them. Those methods are constantly being peeled away, though some are occasionally added or fixed. The net trend is clear. The ability to download is eroding. There have been moments when you might seriously consider that downloading, at least without a complicated setup(PO-Tokens, widevine keys, or something else), is just going to stop working.

As time goes on, even for those rare times you want to grab a video, direct downloading may no longer work. You might have to resort to other methods, like screen recording through software or an actual camera, for as long as your devices will let you do even that.