I remember calling the admissions office to ask if AP or IB is better and when they said "we don't care"
An important thing to keep in mind, is that MIT (as with almost any elite American university) is looking at the decisions that a student took, as a way to understand who the student is and what they might bring to the university. The choices that were made for them, say nothing about the student and consequently have very little value in admissions.
The overwhelming majority of students have no choice as to whether their school offers AP's, A-levels, the IB, the Cambridge Pre-U, or any other curriculuum. As such, which the student took tells MIT little or nothing about the student. Therefore, they literally do not care.
At a more extreme level, consider the case of a student who applies never having taken Physics. The key question is what that tells MIT about the student. A student from a suburban New York high school who elects not to take Physics because he thinks that it might be hard, is giving MIT a very strong signal that he is not a good match. Whereas an international student applying from the fictitious land of Lower Klaxon where the government has determined that Physics should not be taught in secondary schools is giving MIT no signal at all (or at least a very weak one).
The problem most commonly arises with the question "How many AP tests do I need to get into MIT (sometimes how many A-levels?" If you go to a school that only offers 3 AP-classes, you took all of them and graduate with 3 APs, then graduating with 3 is great. If you go to a school which offers 30 AP-classes, and you only took 3 of them, that is suddenly a lot more suspect. The absolute answer is meaningless. What matters is what that answer means in terms of the context in which it was taken, and the decisions that were taken by the student.