It's replicated work for every person who wants to set up filters and notifications. Discord or whatever has defaults that don't require everyone to create their custom environment.
But you trade a lot for not wanting to set up your own custom environment. You only have to set up yours. There is no one size that fits all, and if this flexibility comes with these features mentioned (non-proprietary, federated, archivable, accessible, not dependent on a specific company), then: yes, please! How could anyone not want this?
Nah. The “replicated work” is in deciding what you want your mail folder structure to look like, which is a pretty personal decision; creating the filter on List-Id itself is trivial.