listmonk supports arbitrary nested tags and attributes in the form of JSON. A subscriber can have properties like {"purchased_x": true, ...}. It's possible to issue complex SQL expressions to filter and send campaigns to subscribers.

The multi-list approach has several other benefits. When manager / sender (and other) permissions get introduced, it will be straight forward to restrict users to managing certain lists. In addition, multiple lists allow subscribers to selectively subscribe / unsubscribe from lists.

Internally, the structure is simple. There is only one subscribers table and subscriber data is not duplicated anywhere. List (foreign key) relationships are in a separate table.