I think the correct fix is to stop the anonymization in Mailman. It is largely counterproductive because on the off-chance that some address gets harvested for spam or harassment it is now difficult to conduct any meaningful discussion. And booting an abuser or user who has a misconfigured e-mail account becomes nigh-impossible. I have not seen any other larger project do this.
If someone has issues with harassment or spam due to the addresses harvested from the list, it is easy to create throw-away addresses using e.g. Anonaddy.com.
And re Google Groups - switching to that wouldn't really fix anything, the problem is not Mailman as such but that it is explicitly configured in a silly way. Groups show the sender addresses in the e-mails and on the website too if you are a group member.
J.