You raise some good points, but something needs to be clarified.
Yes, the UX is by and large optimized for those who already know how to use it. But the hiccups that you mentioned are not by design. Those are just a symptom of lack of polish.
As someone who had - as you said - a long career, you will be familiar with the notion that sometimes it takes very little effort to ship a new feature (i.e., something that works in a sunny-day scenario) but it takes a hell of a lot more effort to smooth all the sharp corners, test and add support for all unplanned cases, etc. Non-developers may not have a clear understanding of the scale of this disproportion. It may take one afternoon and a few tens of lines of code to implement a new feature. But it can take many days if not weeks to go from “works well enough for me” to “works flawlessly for everyone”.
In a large software project like darktable, devs do not have a lot of incentives to focus on polish. If a bug does not prevent usage, but just creates some friction, it is difficult to find someone who is willing to tackle it. This is not because devs are evil, but because they prefer to spend their limited time to work on aspects that they care more about, or that for them are more rewarding.