I beg to differ, 7 was actually well optimized. It ran OK on an office PC with 512 MB of RAM and a 512 MHz CPU.

You wouldn’t use that because by that time apps like browsers and office were starting to feel restricted by that little RAM to the point you could only run either or. But the OS itself stayed out of the way as much as possible, and if you gave it just a little more RAM (like 1 GB) suddenly you had a usable office machine.