In the old mailman, the archive overview page would only list months that actually had emails in them. In Mailman 3, however, all months are listed even if there are no emails.

This is very noticeable for lists like WikiNN-l, which is virtually unused – since the first email to it in 2010, there have been a grand total of two more emails to the list. So there are three mails in total, but the archive month dropdown gives you (at the moment) 129 months to choose from. It would of course be better if the dropdown only listed months with any content.

For these completely-dead lists, using the /latest page gives you an overview of everything, so it's not a huge issue. I think, however, that it is a bit more of a problem for lists that were once quite active, but have since gone dry. For instance, you have the Wikinews-l list – it has ~830 emails in the archive, but only 7 of those mails are in the past 5 years. So that's 60 months of archive pages for 7 emails, which is not ideal.

TL;DR: It would be nice if months and years with no emails would be hidden from the archive month dropdown and the left sidebar on /latest.