there's no controllable gameplay sections after that point, just dialogue, shouldn't it end there?

No because you have to hold down an input to get through the dialouge after that

dont quote me on this but i believe it's theoretically possible to mash faster than the wrist protector and get a better dialogue time, so there is time to be saved after the sink even if nobody actually ends up doing it except the TAS

yeah in chapter 2 the game doesnt let you mash faster than wp but the problem is is that you still need to hold down the cntrl/c and shift/x buttons to get through the dialouge. Even if you're using a weight or sticky keys it's still an input. Past the last textbox there's no input needed to get to the credits

Also actually I just realised this is just wrong you need to hold right after the sing cutscene to leave the bathroom and theres more text choicers