BuddyPress.org

For Ousep’s post:

Do I really have to use the bp-sn-whatever template to be able to use any of buddypress's functionality?

No. Just like WordPress has its famouse “Loop”, BuddyPress implements its own Loops for all of the core components and features. See https://codex.buddypress.org/developer-docs/custom-buddypress-loops/.

There is a range of different theme information on the Codex, but you are able to copy all of the templates from the BuddyPress parent theme into any WordPress theme and it will work. You will need to add custom CSS to style those elements, obviously.