(IANA professional computer programmer, but I am an expert on everything, or so that voice inside my head keeps telling me.)

Honestly, I think of UI as the most complicated part of a computer program. Backend stuff is far more regular than any UI of any complexity could ever hope to be. It tends to be easy to model, whereas UI stuff has to deal with the vagaries of human psychology. I also tend to think of UIs as needing to be open-ended, such that it is feasible for the user to do things that the developer might never have considered.

That said, it sounds like your UI might be the opposite of that, and just consist of parameterized views into the existing business logic in the backend. Maybe I'm wrong.

My vision of a UI is complex to develop and difficult to test, in which case your assessment that the UI might be more difficult to develop is probably right, but your solution of requiring more unit testing might be wrong.

On the other hand, if it's a merely presentational UI, then it's probably not that complex to develop and likely pretty easy to test, but that makes your assessment of the difficulty of the task suspect, in which case, requiring unit testing might help, but is probably not the ultimate problem.

What I guess I'm ultimately getting at is that, as an outsider, I'm inclined to disagree with your take on the conclusion here, and say that the two most likely scenarios in my mind are that either unit testing is probably not very productive, or that the development group is not very competent. (I'll qualify that last speculation by saying that it might not reflect on the competence of the individual developers, but might be a political, cultural, or managerial issue. Then again, they might well just be incompetent.)

I'd suggest that you take a closer look at their current testing methodology, and instead of coming at it with your own prejudices and seeing it as the wrong kind of testing, try to evaluate it within its own idiom. I'll bet you'll find that it's lacking within its own internal logic. And getting them to improve or repair what they're already doing is likely to be far easier than trying to get them to change their whole procedure. (Then again, changing their whole procedure might be more productive long-term as you prevent them from falling into old habits.)

Basically, I'm bored and killing time. Ignore me. I don't know what I'm talking about.