It stops being fun when people have to spend 3 weeks on a single challenge because of how difficult it is. It should be fun, not infuriating. This isn't some ultra hardcore survival game, it's a porn game, you do quests and complete tasks, and in return, you get to see a few sex scenes and nude art, but those tasks should not be so difficult to the point where people want to quit the game because the rewards just don't seem worth it for the amount of effort you put in. The game is fantastic enough without ultra-hard challenges like the final sprint thing, and when there are dozens of people complaining about the difficulty of a certain thing, it stops being a thing of people just not being good enough and the challenge just being a tad too difficult for the people who wish to play the game. Some people just want to play the game casually instead of wanting to pull their hair out over a tiny minigame.
But theres a difference between it being a PORN game and eing a porn GAME. the game side of it comes first, and as a game which is actually challenging and needing the player to actually pay attention instead of just have their dick in their hand the whole time, this game succeeds. I love the way he's done it, and honestly YOU should take it as a challenge. Use your noggin. Can't complete the race just by flicking he stick around? Plan out your route, know the hitboxes of the starts, don't try to rush too much or youll miss one, jump at the right times and PRACTICE. That's not a difficult concept. In fact, for the race it kind of mirrors the actual process of getting good at running really. Do it over and over and over again till you mentally know everything you need to do, you're comfortable with the motions, and you finally beat your goal. It shouldnt just be as easy as "HURR DURR ME FLICK STICK NOW GIB SEX SCENE"