Personally I find KP overrated and quite frustrating. Not for the bf, but for the rest. You're told to manage the prison and you're punished for trying to do so. The game punishes you for trying to play the game you've been told to play. It presents you with agency that's not actually there. No matter what you do, she will become a slut, and now you're screwed because everything you invested into trying to avoid that is worthless. Not to mention the entire grind. And it's most frustrating because the art is good. I'm angry at it because I wish it was a better game.
I have my own challenges with Karryn's Prison, but I cannot agree that it "presents you with agency that's not actually there."
It is perfectly possible to keep Karryn pretty much entirely uncorrupted, and finish the game with a virtuous victory. Just build a character that's good at fighting and controlling her desires (i.e. build a character optimized for actually playing the game you're told to play). I didn't spend too much time with the game, but I recall that a Mind+Agility build was a pretty smooth path to a virtuous run.
It is fair to say that a pure run requires a bit
more from the player. A good understanding of the game's mechanics helps, and various bonuses built up from prior runs also pitch in. Yes, it's easier to let Karryn slide into slutworld, the game constantly offers you onramps into hedonism.
That's the central premise of the game though. That's what on the label. Getting frustrated at that is like getting frustrated that local BBQ joint has limited vegan options.
It's also not accurate to say that "everything you've invested in keeping Karryn pure becomes worthless if she goes slut mode." Each of the character builds has some advantages when shifting to a sex combat mode. Some builds are certainly better than others at navigating that transition, but that's an entirely reasonable thing to put in to a game that's designed for multiple playthroughs.
And the author deserves massive credit for coming up with a battle system that can handle everything from wacking prisoners with a halberd, to whacking prisoners off in a stripclub - and all within the same interface, all using the same ability scores, and flow.