I'm happy with my 90s like setup. Films and series in a folder, VLC to play them. I did give Netflix a try but did not like that it only has a browser player and on top of that annoying restrictions.
For better or for worse, legal content distribution has been avoiding PCs as a target platform because of how easy it is to copy and redistribute anything that goes through a PC. If they keep it to more limited set-top boxes like Rokus or SmartTVs themselves, the management will feel like piracy is being prevented.
I was running it on a low-end ubuntu device and the quality was at least 720p as far as I could tell.
One of the main issues with it, at least for me, is that the content is restricted to content here in Belgium. My wife is Mexican and thus we sometimes want to watch Mexican movies or simply see things in Spanish or with Spanish subtitles. Things that are not available on the Belgian netflix.
If you want 5.1 audio, no browser is an option and the Windows store app the only solution.
720p on Chrome and Firefox is also better than your initial claim of "you're probably only getting 480p".
But Plex is really cool for streaming to the phone, watching on TV, watching when you don't have your own laptop, giving access to friends and so on.
I wouldn't want to give up either.