>>58853872USUM is a third version that still leaves locations and planned features unfinished (Ultra City, Gym Creation, Battle Cruise).
Rotom Dex is a genuinely awful use of the 2nd screen compared to XY's UI.
Rotom Lottery is just O-Powers on a slot machine. Instead of letting you select from a menu like normal.
Mega Stones costing BP? Instead of exploring the overworld to unlock them.
Z Moves, flop by Ohmori trying to replace Megas.
No 3v3 or Hordes because the game performance is worse overall.
I do like original SM, but Gen 7 is worse designed than XY in alot of ways. Stuff got cancelled and they were desperate to compete with Yokai at the time...