Levitate and fly would be amazing of course but I'm not sure I see it as a "necessary have".
Maybe I don't know D&D enough to understand why it would be so important.
Aside from the player utility, flight is super important for many creatures in D&D. For instance, dragons are notoriously vulnerable on the ground but in flight are a real threat, as they should be. Even less challenging opponents like imps become far more dangerous if you can’t reach them. And flight is just such a key component of D&D adventures, whether it’s due to spells (incl polymorphing, becoming gaseous etc), flying carpets, winged boots… there are even player races that can fly naturally.