I agree with this, but it was far less clear in the 90s. I think a lot of people (myself included) were expecting/hoping that UIs in productivity software were converging on some sort of finished design or standard that there wouldn't be much reason to monkey around with.

MS Office programs - and many other proprietary software titles - were taught not only in many schools, but also in various vocational programs. You could get 'certified' in having 'mastered' a particular UI, and you expected that knowledge to continue to be useful for years. Seems quaint now, but there were some nice things about it. A carpenter doesn't expect their saws & hammers to radically morph every product cycle.

In the 90s word was still trying to take the crown from word perfect. Everyone knew guis were the future, but the F Keys in word perfect were important to know.

I don't think so, but I also don't think that it's going to be popular opinion around foss/computer people

MS Office software is used around shittton of workplaces and from time to time in day-to-day life, so making people somewhat proficent at it is good for everybody except MS competitors.

I'm not sure what do you mean by teaching "UI" - they teach how to get things done with given software.

It’s hard. I learned a lot of programs (some that don’t exist) autocad and lotus 123. Some of the principals of spreadsheets and vector programs I remember to this day. But having hands on with the software certainly helped learn it.