I sometimes see something like this as a counterargument to the common complaint of the games being too easy: "Yeah, but there's no good way to make them actually difficult". Not that it applies to your post, this is just a general observation vaguely related to the same topic.
On the other hand, if you invert the whole argument, one thing is evident clear as day: It's completely trivial to lower the difficulty of a Pokémon game. Just nerf the levels and movesets of opponent trainers. The only challenge in that case is to ensure the player earns enough Exp. Points to progressively level their Pokémon above those of the opponents. For all the talk about difficulty in Pokémon and how one has to turn to "fake difficulty" to make any given game harder, it isn't often acknowledged that "fake easiness" is not a thing.
With that in mind, it's evident that the difficulty level of the games can be adjusted. Making them more difficult, at least up to a certain point, is feasible by doing the opposite of making them easier. And I think this is what people complain about when they find the games too easy: a few certain recent titles have lowered the difficulty below what's reasonable. Measures such as small boss teams, opponent movepools tailored to be easy to overcome (lacking STAB, focusing on the wrong end of the spectrum, lacking coverage, etc.), an opponent level curve flatter than the player level curve, giving the player access to strong Pokémon that conveniently counter the next boss, other such things. It's unreasonable to ask for Kaizo-level difficulty in a game targeted at children, but it's not too much of a stretch not to want the foes to be configured to crumple up and faint at the lightest touch of any of the player's Pokémon either. Especially after the games added a "use this move!" box that tell players how to win rock-paper-scissors, next to the big, glowing, flashy "click here to win the battle" button.
There is a spectrum of difficulty between "click here to win" and "grinding for seven hours is your only option", and I think it's reasonable to criticize Pokémon for having moved a little too far towards the former. Difficulty-reducing measures have been applied while difficulty-increasing measures really haven't. I think it's feasible to increase the difficulty above the current level without being unreasonable.
I get what you say, on later games we got the buffed exp share which made grinding a non issue but also made the game infintely easier. It was common to see XY playthroughs ending with teams over the 70s, with the OP gift mons like the limited Blaziken event, Mega Lucario (one of the strongest megas ever acoording to this site), the Mega kanto starter, etc. ORAS and the free Mega Lati@s was also very questionable. I'd say SM and USUM had less of this trouble, specially because bosses had EV trained mons that allowed them to hit hard, take hits and outspeed your team; it made me hopeful of difficulty in later titles. Then LGPE came in with the obligatory exp share and SwSh with its broken raid mons...
I'd say grinding was almost never an issue at beating Pokemon games, as long as you know your type charts, the strenghts and weak points of the species and are well stocked, you can take on any foe, which is why "making Pokemon easier" is a baffling choice.
This is a problem that plagues fan games in general, but yeah to be honest my experience with ROMs is that most of them end up delivering a worse experience than the actual games. Story, difficulty, and especially designs... playing them does help put gamefreak's disappointing performances into perspective. Game development is hard.
I have no problem with those games taking a different direction with anime-ish or grittier stories, but claiming that it's outright better that what GF is doing feels pretty disingenuous, since they also have plenty of mistakes in worldbuilding and storytelling. Tropes are not bad, it's how its executed that matters.
Let's be honest: a lot of ROM hacks tend to prioritize pandering to the random additions people constantly claim they want the games to have (e.g. all 151/251/386/493/649/721/809/898 Pokemon, excessive profanity, anime references, "hArD", etc.) over actually making a memorable or interesting adventure.
This is why I dislike Adventures Red Chapter so much. Unlike Reborn, Dark Rising, etc. the plot is held on their own world, but the Adventures romhack exaggerates a lot the "darker and edgier" aspect of the manga. The characters feel very derailed, the later quests were so gory and dumb (the Orange Leaders being the worst offenders), by the end it seems like a mishmash of every bad fan theory while still taking it completely seriously.
To end in a more positive note, I admit even my favorite romhacks (Vega, Prism) and fangames (Uranium, Legends of the arena) had its fair share of flaws, but because game developing is hard it feels pretty rewarding to play a fangame or romhack that manages to satisfy you like the official games do.