Weed out has more than one meaning, definitely the case where you have to get in to the major, but there are weed out courses (maybe not process) even in direct admit majors or colleges. Even in a direct admit program at Purdue or Berkeley EECS, if the students get a bunch of Cs and Ds, since the class is curved that way, that’s a de facto weed out. It also happens in private colleges, I went to private undergrad, direct admit to major, about 20% weed out after sophomore year.