What QOL did they miss a trick on? Character customization.
It didn't even need to be very complex, just... A little better. Some things that would've made things a lot better:
Let the player choose to keep wearing any outfit they've unlocked in the story thus far, without requiring stupid percentage completion. It really bugs me that they started me off with that which I wanted throughout all of EDF - Wing Divers with trousers - and then took that away from me.
Improve the color pallet picker:
a. Let the player enter the HSV values with their keyboard.
b. Let the player save color pallets agnostic of the character class, and thus, load them in to any character class.
c. Increase the height on the palettes so that instead of choosing between 12 colors for channels A and B, we can choose between, say, 36 each.
And, very preferably, make a female Ranger, Air Raider, and Fencer model, and, in fairness, a twinky Wing Diver, booty shorts and all in EDF5's outfit. This would be a little bit more work, but not much - I mean, something like full-fat mix-and-match hat, upper, and lower, with the outfits from all prior EDFs would be amazing, but like... Just give people who only want to play girls a reason to note hate themselves when playing three classes; and give people who only wanna play dudes access to to the Phalanx and the power of flight! (Fencers do not fly. Fencers stomp the ground so hard it rejects them, then fall with style.)