While the idea of a common user interface on computers may have felt like a selling point when facing a new scary machine with a variety of functionalities, did it really save that much time, effort, and learning curve? Particularly with respect to the common office tools it was replacing?

The common user interface was really more a benefit to the company and all the companies which programmed for it at scale. The benefits are like Melvil Dewey's standardization of the Dewey Decimal Classification which allowed libraries everywhere to work on the same system rather than needing to reinvent their own individually.

This sort of innovation with scalability is helpful as humans are far better at imitation than innovation.