It’s true that noat of his romhacks are at the very least slightly harder than their original counterparts, but the one I’d still recommend is sacred gold/storm silver

My sense of difficulty is a bit skewed as I tend to mainly do hardcore nuzlockes, but I recently played through storm silver normally and it was a blast. The gym leaders needed a bit more thought when fighting as each of their pokemon were more powerful, but my ragtag group of 6 I ran with only ever failed once in the whole playthrough, and that was against the elite 4 (so somewhat expected)