IMHO, the peak for UIs that are easily usable by regular people with minimal training was back in the mid-to-late-00s. It was before this idiotic flat-UI fad, when UIs had a colorful 3D look to them so they were actually attractive, and also functional (since they were also very discoverable). This was just before everyone suddenly decided that PC UIs needed to be the same as those used on small touchscreens.
However, I will say those 80s mainframe interfaces were extremely functional. For someone who had taken the time to learn it, they could get work done really quickly.