Normally yes your right (especially with many2many) and for tags yes it’s generally a good idea to use the manyWay but the downside is the analytics as you’ve figured out.
In your case, honestly a custom controller and directly accessing the database through custom queries (either mongoose or bookshelf depending on your database choice) is the better option.
You could build the controller and build a GraphQL resolver for it, but that’s really a lot of work for just an analytics response. REST in this case is much easier.