The 6 year graduation rate for ivies ranges from 93% to 97%. It is certainly uncommon to not graduate, but that is quite different from saying it is very difficult to fail. The ivies generally admit stellar students who are extremely unlikely to fail out at which ever college they choose to attend. If the ivies did not have an extremely high graduation rate for such students, something would be catastrophically wrong. If you look at predicted graduation rate based on stats of the incoming class and compare to the actual graduation rate, a few of the ivies actually have a lower graduation rate than expected (depending on methodology).
Plenty of students at such colleges do not need an extra year and tutors for tough majors, including athletes. For example, in the 4 years I was an on-campus student at Stanford I completed a bachelors and master’s in electrical engineering, and also started on a 2nd masters in a different engineering field. I did this while being on a sports team (not all 4 years and not while working), having part time jobs, starting a small company, doing the pre-med track, etc. That said it is common for athletes in certain sports, like football, to redshirt one year and graduate in 5 years, but the reasons for redshirting are generally not driven by major choice.