I like that you emphasize knowing your users. Why is WordPerfect around today? It's because for certain types of users (typically legal offices), it does what they need to do far better than Word. Would I use it? No, I'm not in a legal office and don't need those features.

You can look at the origins of the two programs. Word was aimed at "typical" users who are not, for the most part, full time document producers whereas WP was aimed at document professionals. Word made things that typical users do all the time easy with simple keystrokes, WP tended to group things functionally, so related functions would use the same function key but with different combinations if modifier keys (Shift, Ctrl, Alt). For a full time document producer, learning these keystrokes was worthwhile. Many of these functions in Word would be buried deep in menus, if they existed at all, because its typical users didn't use them.

Both tools were, to some extent, following what you have described, but they came to different conclusions because they had different target users.