Definitely not auto-admit. Your chances might be slightly better than the overall acceptance rate.
There are indeed a few applicants who are not qualified, but only a few. MIT tends to draw very well qualified applicants, and still has a low acceptance rate. MIT is not exactly the place where you expect there to be a lot of students who were accepted based on their athletic ability, so you are not going to lose out to academically mediocre super-athletes.
However, MIT is definitely not a safety for nearly everyone.