Using F-keys for the most shortcuts was standard across DOS apps. As far as discoverability, the common UI pattern was to show a single row of function key labels on the bottom of the screen (and update it when the user pressed and held Shift/Ctrl/Alt to allow for combinations), often with an option in settings to hide it once the user has gotten accustomed to the shortcuts.
I don't recall any issues touch typing F-keys, either, especially on typical keyboards from that era which had the entire row split into groups of 4, making it easy to find the right key without ever looking.
I'm not sure what you mean by "much less muscle memory involved" wrt F-keys. I still, to this day, have muscle memory of F2=save from using Norton/Midnight Commander so much.
Better options didn't exist. Wordperfect was expected to work on a 4mhz computer with a low resoluion screen and be fast. f keys or contorl shortcuts - both were not good options but given the constraints fkeys are better - f keys had a place to put your cheet sheet.
I don't recall any issues touch typing F-keys, either, especially on typical keyboards from that era which had the entire row split into groups of 4, making it easy to find the right key without ever looking.
I'm not sure what you mean by "much less muscle memory involved" wrt F-keys. I still, to this day, have muscle memory of F2=save from using Norton/Midnight Commander so much.