I find this a bit questionable. What are some examples of this good UX and UI? Many HTML-ish UIs I can think of are not good. Slack, Discord, modern Windows apps such as the new settings app for example. They tend to suffer from poor reimplementations of native widget functionality, poor implementations of scrollable elements especially infinitely scrollable ones, low information density and too much whitespace often exacerbated by flat design, janky responsiveness often with high latency.
Maybe there's some abstract notion of "good UI" that is distinct from "people like to use it". Or maybe people are stupid.
But on a purely empirical basis there is absolutely no evidence for the supremacy of the old UI paradigms you champion.
In any case you're right, I think there isn't enough study into these things.
I much prefer finding my way around any "badly designed" UI that can respond in 20-100ms a "well designed" UI that responds in 500-5000ms.
Most web software providers don't (can't!) deal with server latency or the client-side processing of the JS/CSS etc. that they use. That's why I use a lot of "well designed" UIs that respond slower than equivalent systems from the 1980s.
"Modern" UIs are often atrocious, and I'm not the only person who thinks so.
Feel free to join in :-)
Though I'm on the side of classic menus in the infamous ribbon dispute.
However I'm pretty confident that if I show such an interface to non technical people, they will feel that it doesn't look nice, compared to whatever proprietary app they use on their phone, Windows/Mac, ...
I personally don't use Word nor LibreOffice (I use mostly LaTeX), but if we want free software to become more popular, there must be a focus on the design.
There is also a search feature now, so its not like you need to know where rarely-used things are.
Just also give me keybindings and let me hide whatever ui you make.
So, why you'd you contact him and tell him where he's going wrong? I'm sure he'd value your insight and guidance.