As the dungeons go on, balancing becomes a lot more difficult. Level difference start mattering less and less, so the difference between the player at the start, and at the end of the combat are much lower. You should expect balancing issues to exist in new dungeons more often now. I still hope to one day add an actual hard mode where I don't have to care about handing out a casual experience. For this one though, I think I'll move the pony gear to give DEF upgrades and increase the attack of the enemies, that should work. I might get rid of the good horse / bad horse thing alltogether.
For dungeon 7, I like the idea of an infinitely repeating training area with some of the gear delivering enemies at the side. I'll also add a full loadout in a chest somewhere. I don't think the blinders are a problem though, since it requires your entire team to be equipped with blinders before you are completely vision locked - otherwise it's just a way to force you to change your first partymember - and as you mentioned, that is unlikely to happen unless you opt-in for it. Finally, I'll also make it so Grace accumulates just from walking around in ponygear, that should also make the boss more difficult.
From both your posts I've also made the plan to implement some changes to other dungeons. I'll be adding some shortcuts to 4 (make the metal bars open from one side), as well as an extra move for the enemies and players at high mummification. For dungeon 5, I plan some more flavor text and moves for penis envy, as well as harsher drawbacks for wearing a cramped chastity belt. I had a look, and unfortunately adding new dungeon specific stats breaks save compatibility, so I'll just opt for adding plugs with more diverse effects rather than an anal training stat.
As always, thanks for the feedback!