> I find it almost beyond belief that someone with a [supposedly] large amount of experience in software development would to think that allowing clients to implement UI themselves is a good idea.

It's not at all strange as there are many different types of UIs that have to be built.

I think what the author is thinking about is the typical CRUD applications that many businesses need and that are only built in-house, where the UI matters less than in consumer software, and the UX is still important but as long as it's changable, could be done by the users themselves.

I feel like the UI you're thinking about is the one for consumer software, where you're innovating on some solution for a particular problem, and the UI/UX of the tool is probably the most important thing, otherwise people won't pick up the tool in the first place.

If you look at the output of many software agencies, most of what they are producing is simple CRUD applications (and some startups do this too, I guess) which probably could be built by the users themselves, if it's basic enough. While the output of the ones building B2C software is slightly more complex and requires more thoughts behind it to even work out.