What genre could Interstellar be said to be 'one of the top movies' in? Certainly not sci-fi as a whole; maybe some specific type of sci-fi.
As much as I love sci-fi, it isn't exactly the "strongest" genre out there. I'd say
Interstellar is a top ten, maybe top five sci-fi movie based on how "good" it is. It's my personal favorite, but I can acknowledge that
2001, for example, is "better" on the "good" scale even though it's a chore to sit through and doesn't have half the heart that
Interstellar does (not to say that I don't admire
2001, though). I'd grant you a few other classic sci-fi films similarly, but not that many before the balance tips. Certainly not enough to push it out of the top ten.