It's not hand-holding that bothers me. I don't recall being bothered by that at all.
It's the SOS battle system which makes catching Pokemon so much more difficult since there doesn't seem to be a limit to how many times a Pokemon can call for help, making it impossible to catch the Pokemon. It also double teams Pokemon when you're wanting to train. Training Pokemon in S/M is so annoying and tedious that I actually went with the Exp Share on almost the whole game because I couldn't stand to actually train Pokemon individually with how bad it was.
It's how all over the place the difficulty felt. One minute I'd be battling a trainer with AI even worse than previous Pokemon games, the next I'm dealing with a trainer with actual good AI and Pokemon that's stats seem tampered with, making my Pokemon's attacks much weaker than they should be, and making my Pokemon KO'd much easier, as well. I find no fun in that. I'm not a competitive player, and I don't want to have to train and breed my Pokemon like a competitive player to be able to clear matches. People can play competitive if they want, but that should not bleed into the actual quest of the games.
I didn't like how limited the region felt. There were so few places to surf, fishing is now only allowed in certain spots, etc.
Also the removal of the National Pokedex. That just really did me in. Collecting Pokemon felt pointless. The AR feature where it shows you a number of Pokemon not in the Alola Dex was rendered completely pointless because those Pokemon seen don't register anywhere in the game.
I don't know what US/UM are like, but I'd wager they don't improve upon any of these issues. I'm not going to spend $40 to find out.