I've found that ideally all product changes should be developed in close collaboration between a product owner, a UI/UX-person, and a developer. The design shou

I've found that ideally all product changes should be developed in close collaboration between a product owner, a UI/UX-person, and a developer. The design shouldn't be made upfront and handed to the developer, it should be made iteratively with the developer providing feedback. And the same goes for the product owner, giving input about user needs and their mental model. The developer should provide feedback about what is feasible and easy instead of just being expected to code up a design that's thrown over the wall. If you allow any of these parties to do most of their work before the others, then you'll get a local optimization that will either constrain the others to do sub-optimal solutions for their areas, or force the final result to break out of the optimum from the first area. The best result comes by having each side provide input in each iteration. Getting a team to work like this is rare though, in my experience - I guess that's part of what makes unicorns so valuable, since they'll integrate several of these roles in one person.