Looking at other newsletter plugins I partly agree: Lists can be confusing.
What you wrote is probably true, Brian: Many site owners will only use one list — the big one — to send out newsletters once in a while. So lists would be an extra feature fpr them which they would not need. In a ideal solution more than one list could be “hidden” as long as this feature is not activated.
Even though the backend of the plugin “Email Subscribers” is a mess regarding intuition and user friendliness the software offers a rather good list approach: The admin can decide what list(s) a subscriber will be added to — meaning: no choice for the subscriber.
As a second method Email Subscribers offers the subscriber to chose from a list of lists defined by the admin. (The subscription form then gets rather messy: All these checkboxes and the GDPR consent are confusing.)
You mention custom field as a possible criteria for sending out newsletters. I cannot comment on that because I have no idea how this would work. Being limited by the bubble I live in (regarding newsletters) I would probably prefer subscribers who are “members” of one or more lists. Email Subscribers solves this with the typical WordPress approach: category-like.
Did I miss anything? Well, maybe I didn’t describe the point very well that made me thinking of lists. I will try in a few sentences — even though I am aware that you know what the list thing is about. Sometimes a real life situation helps:
My latest online project is about saving historic buildings that are endangered. Building a community is the first step — and a regular newsletter for this community is a must to keep people informed and involved.
In a second step we will have more and more buildings online that are endangered reported by various people. Some will set up a petition. Such a petition needs immediate awareness and it is not a good idea to tell the community only in the next newsletter — which could be in several weeks. This newsletter has to be sent out as soon as possible. “Regular” newsletter recipients could consider this as spam due to a higher frequency.
So something like a “Petition Alert” list would be a good idea.
Overall: Yes, it is complicated and I don’t know a newsletter plugin that solves this in a convincing way today. (I kept away from paid services like MailChimp for reasons of privacy. Maybe they offer their own WordPress integration which is close to perfect? I simply don’t know.)
So much for the moment — this got way too long for 1 am. Please excuse my talkativeness. I am tired.
Cheers, Frank