Yes. Though to some degree no because the API strongly guides/restricts the UI. The UI is the only thing users are concerned about but the API is what makes good UI easy and robust. I implemented some UI I like in JS in spite of the 90s “API” after realizing I had done little but whine about it; and HTTP is HTTP whether there is a sane API behind the responses (POST/GET, meaningful status responses, well-behaved and modern charsets, no hidden variables picking form behavior/endpoint, JSON responses, etc) or not. :P