Easy way to delete 70k posts and attached media?

If you know how to find the posts, then we can use WP CLI to do a 2 step process.

First, grab all the post IDs in those categories using wp post list

E.g.

posts=$(wp post list --field="ID" --category__in="1,2,etc")
wp post delete $posts --force

Then we can plug the values in posts into wp post delete.

We can also use the same trick to delete the media, via the post_parent__in parameter to fetch their IDs, then deleting them.

If you can’t run WP CLI directly on the server, pull a copy down to you computer, run the commands, then replace production with the result