The hitsounds are fine volume-wise? I think people are saying they can't hit them because they blend in too well. Try adjusting music volume to 0% and listen.Volume wise they're quite loud yes, the blending is an interesting situation as it seems to only affect some.
Ideally for people who are having it blend / can't discern the individual sounds, when they start drifting off beat due to lack of feedback they'll start to hear the sounds again. Then hopefully when they recognize what the hitsounds actually sound like, they can start listening for that in the music.
Not sure if it's asking too much of the player to listen through the blending in these specific cases, but my options are pretty limited, barring redoing the entire map's hitsounds...
I can turn up the volume in these cases, but that will make it too loud for others.
I think it would be fine for people to simply lower their music volume until it is comfortable? Now that changing effect and music volume is so easy thanks to the dials update.