BuddyPress.org

The only way BuddyPress is going to upgrade without being a pain is if you either use one of the bundled BuddyPress themes as a parent, or use another framework that is kept up to date.

If you build a theme from scratch built on a copy of another theme, or do not create a child theme from a parent that is kept up to date, you are going to have a bad time.

This will always be the case, since BuddyPress is a tight combination of plugin code and theme code.