I agree with you but the Raspberry Pi's USP is the GPIO interfacing capability and the community surrounding it. You don't get these things with a second hand computer.
Rather than using DietPi for my devices around my home I use Balena (balena.io), which seems to cover the same area. In addition it has a dashboard so I can see the status of the devices too. Balena is Docker based. No connection with Balena, just a happy user.
It is interesting to see the ESR (Equivalent series resistance) of the capacitors replaced too. This can be more significant than the absolute capacitance.
Currently a Back end C# Dev here, 65 year old, so not old yet, I also exercise regularly 2 * Body Pump, 3 * Body Combat, 2 * Sh'bam, 1 * Body Balance. I find the group exercise classes keep me sharp for work too.
Raspberry PI OS 32bit is compiled for ARMv6 to support the orginal Raspberry pi. I wonder what impact on benchmarks there would be compiling for ARMv7 hence only supporting Raspberry pi 2 and later?