Everyone has his own way to configure and use their music library, and I am aware it’s difficult for Roon to deliver a complete framework where everybody can define all own wishes.
Your suggestion works probably if an entire album is acoustic, which is not always true.
As far as I know it’s not possible to create genres at song level.
The way Focus now works “AND” & Tags OR is confusing.
In the meantime I’ll be waiting patiently for crazy ways Danny suggests :