The consistency of a UI is quite distinct from the quality or the usability of a UI. You're incorrectly blurring these very different concepts. I never claimed

The consistency of a UI is quite distinct from the quality or the usability of a UI. You're incorrectly blurring these very different concepts. I never claimed that all UIs back then were "perfect", or that there weren't "badly designed" UIs. I was very clearly talking about consistency between different applications running on the same system. When using applications from that period of time, one could expect to find a menu bar and menus that were quite similar to those of other applications. Of course there were application-specific menus and items, but there was at least a common subset shared by nearly all applications, especially any that were designed with even the minimal level of care. The same held true for toolbars, keyboard shortcuts, common dialogs, and so forth. There were also general conventions for how the application-specific parts of UIs looked and behaved. While not everyone followed these conventions, of course, most of the major and seriously-designed applications did. We have lost much of that today. It's particularly bad when it comes to mobile apps, and getting worse when it comes to desktop applications. Yes, Microsoft and Apple themselves are to blame, to some extent. But it goes much beyond that these days. Inconsistency is the norm, and that does lead to inefficiency.