With the new RVSM airspace, the vertical separation went from 2000' vertically to 1000'. Without a functioning A/P among other things, you can't operate in that airspace.
Two guys on a clear, smooth day, no problem The rules are there for the guy who's been awake for 18 hours, at night, in moderate turbulence, in clouds deviating around storms and receiving a clearance change while the other pilots in the lav and the senior FA is in the cockpit trying to show the pilot her picture wallet of her kids (actually cats 😉 )