I have 4 machines (2 desktops, 2 servers) with 10+ years of just being updated, plus few hundred that have 5+ years (we migrated to Debian at work few years ago after using Centos; best decision ever, thousands of lines of code in configuration management removed that were just fixes for centos stuff..)
I'm glad to hear the Debian update process is smooth, as I'm getting started building a homelab this weekend with Proxmox (Debian-based). Definitely don't want to completely reinstall my hypervisor on a regular basis!
Fedora is also usually pretty easy to upgrade between releases these days as long as you follow the instructions.
RHEL's model is similar to Sun's old model. You sell a small, stable core OS that is well supported for it's lifetime. You are supposed to use it until there is an new version then start using that with the plan for the systems using the old OS to retire. IE. upgrade path is whole-system based and it really isn't designed for upgrading in place.