(I'm working on a HGSS romhack myself, so reading this thread is very insightful!)
Another thing that romhacks frequently do with HMs is allowing you to use the move, even if it's not learned by anyone in your party, so long as you have a compatible Pokemon with it. This is definitely a QoL decision I can get behind, and it leans into the idea that this is something your Pokemon is physically capable of doing. (sadly, it is also a feat that's kinda outside my hacking capabilities, but that's besides the point). Personally, I'm someone who just straight-up doesn't like HMs as a mechanic, but this is the best compromise I've observed personally between having HMs and nixing them outright.
Personally, I don't mind when romhacks make drastic changes to Pokemon, because ultimately it's an experience you just won't get from the main series. I think there's value in being meaningfully distinct from what you'll get from a mainline title. While I can subjectively disagree with some changes - for example, it's very common to make Flygon a Bug/Dragon type, which I dislike since the Ground type is pretty key to its flavor and lore - I can appreciate the fact that by using a Bug/Dragon Flygon, I'm ultimately getting a different experience than what I ordinarily would have in a regular Pokemon game. Of course, changes for the sake of changes are pointless - like, I'd definitely get a different experience out of Charizard being made into a Rock/Ghost type, but that doesn't mean it makes sense. It's a hard line to walk, though - what makes sense to you isn't going to make sense to other people, and if you go too far you'll kinda warp the identity of the original 'mon. This was actually put into perspective for me when I discussed some potential type changes in my own romhack with some friends - they (rightfully!) observed that I was often making silly changes to monotypes with some pretty flimsy justification just to make them unique. I'm sorry to the Just a Seaking of one week ago, but Fire/Electric Magmortar is dumb as hell no matter how you try to justify it.
Ultimately, what I like most in romhacks is really the convenience of it all. Version exclusives, trade evos, and other products of a bygone age are by-and-large just gone outright, HMs tend to be modified such that I usually don't have to teambuild around them, and various other QoL features just make the experience a lot smoother. Unfortunately, I'm an adult who's gotta pay the bills, so I appreciate that romhacks implement convenient stuff like grinding facilities and EV/IV checkers - it's a lot more respectful of my time. That's not to bash the people at Game Freak - ultimately, they're the ones who made the original game and assets to begin with - but I do really appreciate the presence of romhacks, even the simple ones that up the challenge a little bit and make life a bit easier.