Have seen Interstellar a few times in the last several months and am inclined to agree with you that it's a great film overall but not a classic. However, it is possible time (heh heh) will improve our opinion of it. When Roger Ebert first reviewed Spielberg's A.I. he said there were good elements in it but he just could not consider a masterpiece. Before he died in 2013, he put it in the fourth and last of his books of Great Movies. It took twelve years for Ebert to change his mind on AI (maybe less). Perhaps in another five we will have come to the same conclusion with Interstellar. Now, Tenet on the other hand...but that's another article which I have little doubt you've either already written or will write ;)