U-smash imo fills the same purpose as AC D-air, except you can charge U-smash, and it's disjointed enough to sometimes beat out a few things horizontally.
Also if the damage to shieldstun ratio is 1.25 like @
Shaya
suggested, then I believe Ganondorf's uncharged U-smash is -5 on block lol. Won't happen often, but funny to know.
Also, N-air may in fact be just -9 or -13 on block if spaced well (factoring our N-air has 18 frames landing lag, and does either 12 or 7 damage). Seriously, I believe Ganondorf actually benefits a lot from shield stun mechanics in this game.