Re: Uninstalling BP
“BP seemed to move it into /blog/ subdir.”
BuddyPress did not move anything in your installation, even If you defined BP elsewhere than main blog,
Backup database, deactivate BP and BP-dependent plugins, then go to your database and delete around 15 tables with : yourprefix_bp_componentname
If you need to move WP to root, https://codex.wordpress.org/Moving_WordPress – as always, back up your database before attempting the move