Not at all. I'm not proposing anything that changes how permissions apply. Allow me to explain what I think Mailman needs wrt List Admin functionality.
Mailman is widely deployed in commercial "shared web hosting" environments, under cPanel control. Customers of such services – and this is the single most popular form of recreational and small business web presence -- don't run their own Mailman instances, and don't have any sort of command-line access to the Mailman server, much less root. Where such Mailman access is provided, either cPanel presents the user with the interface to create lists (and handling the business logic of limiting or charging for lists), or customer service creates the list for the customer, manually; the customer is a List Admin, but they are not Site Admins. Their list appears to be at firstname.lastname@example.org and the Mailman interface is available somewhere at http://theirdomain.tld; it is owned by the owner of theirdomain.tld.
Such a customer is the List Admins for any lists they create at their hosting company. As such they might reasonably want to perform any of the following tasks which are presently not things Mailman directly supports:
1) They might want to backup their list's settings, membership rolls, and archives. A customer might reasonably not trust their hosting company to do backups of the listserver right. (And let me here just allude to the time the company that was donating server access to the non-profit that hosted a list I was on suddenly went bankrupt, and for a week while the server was shipped cross-continent by UPS we had no idea what happened to our list, and no way to recover the membership rolls, etc.)
2) They might want to take such a backup, in a machine-readable form, and be able to submit it to the Mailman interface for a list and have its settings, membership, and/or archives restored. Manually entering all the settings for a Mailman list is, yea verily I am the voice of experience, really quite a lot of hassle, and error prone. The membership and archives can't be manually entered. There is no way to upload archives, and while members can be subscribed, resubscription through the mass-subscription tool loses all sorts of information. It loses just who had previously be set to moderation (ask me how I know!) It means all subscribers that set themselves to no-mail and all subscribers who were automatically to no-mail due to bouncing, are now down as set to no-mail by administrators: so after a move, anyone who might previously have set themselves back to getting mail, has to get a list owner or moderator to do it for them, like they didn't have enough to do.
3) They might want to take such a backup and use it to take their list (email@example.com) with them when they move theirdomain.tld from one Mailman-offering host to another. I've now moved certain lists twice in this List Admins role as part of a domain move, and at no point has it been any fun. I am profoundly grateful that I did not get Mailman service from CornerHost, at which I was a customer when this particular fiasco happened: sometimes people have to move off servers when the people with root aren't answering support requests.
I'm not suggesting that anybody have the ability to upload to a server they haven't been granted the authority to. Merely that there should be web interfaces to allow upload and download of data files for things they already have permissions to read/write.
Please consider this suggestion. It affects what I gather are a rather huge number of Mailman List Admins and the way things presently are makes more work for staff at hosting companies and means the many users who are List Admins but not Site Admins are disenfranchised from their data.