I have a Colt sporter in 5.56. I guess you'd call it an 'A2', no removable handle, no bells, no whistles, no rails no optics but iron sights, nothing.
I've never served. When I wanted to buy an AR I took along a friend who did serve, US Army. We looked at a bunch and he picked up the rifle I have now, and said "you want this one"
He taught me to use it in 30 seconds, and the instructions he gave me stuck in my head. From completely untrained to being able to use the rifle even if it jams (which I haven't had happen) in such a short time tells me that there's something 'right' about the rifle, regarding ease of use. It's easy to use and easy to shoot, and easy to be passably accurate with
That's not the classic 'ergonomics' as we think of it today, but easy is still easy