From a workflow perspective I agree with you, it makes complete sense for a single developer to handle most of the development work and have that intermediate step (i.e someone that just builds UI). I personally believe that the UI designer should be doing the front-end work whereas the engineers build the integrations.
Another thing I was getting at is what you mention in your comment. You know about a lot of things as an engineer; and in that role it makes sense that you should. But it feels as if a lot of that responsibility is moving towards the front-end developer now. It's not necessarily wrong; perhaps front-end developers should be learning these skills; but then we have to standardize it or the list of required skills just becomes too long.
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