Looking at the last month of mailing lists which archived mails, we have about 120 email out of 700+ email lists which got at least one email. The 40 most active emails in August to beginning of September were 

  36148 scm-commits
   2178 package-announce
   1737 go-sig
   1729 package-review
   1163 rust-sig
   1145 python-sig
    864 devel
    786 releng-cron
    676 gnome-sig
    449 epel-package-announce
    441 perl-devel
    419 neuro-sig
    344 users
    318 epel-packagers-sig
    317 infra-sig
    313 kde-sig
    313 arch-excludes
    289 container-sig
    229 test-reports
    192 deepinde-sig
    186 ruby-packagers-sig
    156 virt-maint
    151 kernel
    141 fedoramagazine-tips
    126 freeipa-users
    124 perl-maint
    108 epel-devel
    104 rpm-software-management
    102 openstack-sig
    101 meetingminutes
     98 test
     97 i18n-bugs
     97 certbot-sig
     86 kexec
     75 java-sig-commits
     67 dns-sig
     50 nodejs-sig
     45 lvm2-commits
     45 infrastructure
     44 389-users

I am wondering if some of these lists would be better using something like public inbox https://lwn.net/Articles/748184/ like sourceware is using https://inbox.sourceware.org/. Various announcement lists and things like scm-commits do not need to have interactive webpages like mailman3 hyperkitty give since they are limited to few people.