I did LOTS of research on what firewall/router distro to install to my new router a few months ago. See my comment history for considering different options.
I have to say choosing OPNsense has been a great choice. All the things you said I can agree on, but I have to add one more thing:
That quick search bar on the top-right corner where you can quickly type where you want to go. That thing is just super nice when jumping through places in the router.
Now if I'd need to build a new router, I'd like to try my luck with NixOS. Would be great if I could just build a new router from a reproducible configuration.