Google groups is also the mechanism for defining groups for viewing/editing permissions, comments, calendar invites, etc across Google Workspace and for access permissions in GCP. That group definition aligns nicely with being a mailing list grouping. Those use cases are not going to go away, and I would expect Google will invest in them more (as Workspace has been an area that Google has significantly invested in, and I'd argue has been doing a good job).
I think this is a key point that many people don't realize. The ACL groups and mailing lists you create in Google Workspace are the same groups you see when you go to groups.google.com. This is absolutely integral to Google Workspace as you point out and isn't going anywhere.
