all the add-ons and extra user stuff

You're hand-waving the answer to my question :-) What add-ons and extra user stuff require Home Assistant to be an OS?

If you did all that as a package install, you would complain about all the dependancies and if you didnt install the right version of something Home Assistant might not work at all

That's not how packages work. The packagers take care of all that. That's the point.