I disagree that UI/UX as interface design is where we lost the plot. After all UI mostly refers to the looks and UX to the interaction, both have always existed

I disagree that UI/UX as interface design is where we lost the plot. After all UI mostly refers to the looks and UX to the interaction, both have always existed and on their own are certainly not bad. For me one of the biggest issue is that neither the developer, nor the UI/UX designer are actual users of the software they write. If you don't actually understand how users end up using the software, best even skip the interviews with users, you'll never be able to write software that truly serves the users. Additionally, you have the separation between developers and UI/UX which leads to another area where trade-off needs to be made to accommodate (new) requirements. In that sense you might be right, that when the developers created everything, they were able to shape something way more efficient and concise, but often also at the cost of looks and potential accessibility. A second issue I see is, that software these days is always developed for the average user, where as in the past software was developed for experts. As such the look becomes "simplified" and the UX dictates a layout that is cumbersome to use for experts and power users.