This isn't as true as it used to be. My current Jellyfin server is an old laptop with a 5TB USB hard drive dangling off of it. Syncthing is used to sync the media to another system in my house because I don't really want to rip it all again if something fails.
If you proactively torrent "everything I may conceivably ever want to watch" or are glued to media 12 hours a day but still want it all to be new, then 5TB will go quickly, but 5TB can go quite a ways for people who don't match those conditions.
While a NAS won't hurt anything, the days when you needed one to do anything useful at all are gone. Just like I just slam my entire MP3 collection on to my phone's SD card now... I don't need any sort of windowing setup, or network access, or anything fancy anymore. Not only does it fit, nowadays it's only a fraction of the space anyhow.