Also highly disagree that Chat was the UI. ChatGPT only blew up in mainstream because people like the idea of being able to "talk to a computer." If it was agentic from the start and worked in the background, LLMs wouldn't get the kind of marketing push they got in the mainstream world (filled with non-programmers).
In terms of UI, of course its terrible to do anything functional repetedly. Imagine having to ask your car to do a right turn really fast, waiting for it to reply while the car speeds away vrs actually having a steering wheel.
ChatGPT was brilliant in terms of making normal people really get into the idea of "oh wowo my computer is a human now"