MIT Mystery Hunt 2020/Harvard Ballooniversity

Harvard Ballooniversity is the metapuzzle of the round of the 2020 MIT Mystery Hunt.

Puzzle Elements
Metapuzzle (Shelled Meta) - The puzzle has two parts to its shell: an image depicting the balloons from the round art and a catalog of classes.

Flavortext - This salesman is living nearby and working at the park while taking classes part-time at Harvard Ballooniversity.

''He says that he's just hanging on (balloon joke, there), but that he'll be fine, and that there's no "F" in "Harvard"! (Well, at least they call it something else.)''

He tells you his intended major, but you get the feeling that he's facing a problem once he gets down to earth… what should you tell him to watch out for?

Hint in Flavortext - The hints come mostly courtesy of the second paragraph, which not only tells the solver about Harvard's slightly different grading system (using E instead of F), but also that said grading system factors into the puzzle. Later down the line, after learning the balloon vendor's intended major, the third paragraph clues to undo the effects of the grading system.

Association - Each class can be associated to one of the feeder answers. The classes can then be ordered using the balloon art.

Transformation (Letter Replacement) - Here, solvers need to realize the punchline to the flavortext: the balloon vendor is referring to the rampant grade inflation problem at Harvard. Replacing the letters B, C, D, and E in each answer with As provides another valid word...

Association - ...which can also be matched to one of the classes.

Indexing - The solver can then index the number of units in the class into the grade-inflated answer to obtain AVIATION...

Once More, With Feeling - ...which, while a good candidate for a balloon vendor's major, is not the answer. The third paragraph hints at undoing the grade inflation; replacing each A with the letter it replaced in the original answer yields the final answer.

Asked and Answered - A double feature—both the balloon vendor's intended major and the problem he should watch out for are provided by the puzzle.