When I eventually rebuild things I’ll be going with Debian.

Unfortunately Debian wouldn't be exempt from "network interfaces renamed, lost default route, systemd timeouts taking 5 minutes, etc." because systemd is systemd (and Debian systemd maintainers just go along with upstream and do nothing to mitigate it)

I think interface names changed like at least 2 times in the last 4 releases.

Maybe? I run Debian on several VMs and my experience has proven otherwise. Major upgrades go a lot smoother than on Ubuntu.

Smoother, sure. I'm talking about interface name changes. it's nice you haven't encountered these releases but they sure happened in Debian, too.