For me, it started with 10.7 when a lot of things changed just to look different. From then forward, user habits were seemingly not considered and everything moved here and there on a yearly basis.
At least with Windows, the major overhauls to Explorer come so slowly that your productivity routines don't get sand in the cogs every year when you update and Apple's OS shifts extremely key parts of the window UI around and makes the hit points even smaller over time.
The killer for me is how difficult it is to fix things if you don't like them. Modern macOS has horrendous mouse speed handling, and changing this beyond Apple's very limited settings is a pain. And even then, Windows and Linux and older OS X handled the cursor movement better. I like(d) so much about Apple over the years, but it is clear they're an iPhone company that makes laptops and desktops... not the other way around.
Be aware this equipment is not pleasant to be around (loud, hot)
Server hardware is too heavy/bulky to be able to support a big online marketplace. Your best bet is to identify the type of organizations that buy the server hardware you want to buy used and find out how they get rid of their excess.
I've gotten a handful of free server equipment (no drives) by being willing to show up and take whatever is being offered.