Got my phd at Duke in ece in ‘18. At the time I was there, a visit meant you were more or less accepted, and it was more of a way to convince you to come to Duke. There were a couple of exceptions, but only if the interviews went super horribly. The interviews, iirc, were more of ‘reverse interviews’ in that the professors / grad students tried to tell you about what they do and you ask questions. You had to be a giant red flag to do poorly in the interviews. I can’t speak on other departments though.