Can't really speak to a length preference, I'm not really looking at any of the designs from the standpoint of modesty or fashion style. It just looks out of place in the design to me. Like a curtain stapled to a car.
I have to agree with you. It's really not a matter of length. I just think D's skirt just looks plain, awkward, and purposeless.
The fanart is way better, but only because of her expressions and the creative use of her hair... not her clothes.
I voted for Call E, though I'd be happy with Call F, too. I don't care if they lengthen her skirt a bit to satisfy people who cry sexism. Her outfit and her expressions fit the role of a "Call" with personality. I imagine that a playable version of her would incorporate transformations and alternate outfits... they have a lot of creative freedom with 3D models, after all.