I am fascinated by your user friendliness experiment and I often daydream about conducting one myself. I would be interested in reading a more detailed write-up of the advantages and disadvantages of each option.
For Debian, did you consider setting up unattended upgrades?
Would you consider adding an RHEL/CentOS derivative such as AlmaLinux to the mix? The current version of AlmaLinux is supposed to be supported until 2032. The EPEL repository brings the software selection a little bit closer to Fedora.
I wanted to do some stress testing on a gaming laptop a while ago and many people recommended OCCT. The laptop was still running Windows at the time, so I tried it and it seems like a good tool. It tests the CPU, RAM, GPU and power supply. I wasn’t able to find an equivalent in Linux.