Well, that's the question - does it actually do so? Or does it do so in all cases? To use the old example of the quantum ogres that will be encountered whether the PCs take the right or left fork in the road - if one direction is reputed to go to ogres and the other is supposed to be safe (for some reason), then maybe yes, it would foil the agency of the players trying to avoid the ogres. But if the choice of left or right is otherwise meaningless because of lack of information, does it really do so? Suppose the PCs want to encounter ogres as soon as possible to fill out their scavenger quest card (because they're racing against Team B: Shrek's Irregulars who already have ogre checked off on their list). Then isn't serving up the quantum ogres supporting their agency and choice to encounter ogres?
But then, what if the situation is pre-written and thus not "illusionism" and the reputedly ogre-free path is actually a gambit by an unusually clever ogre to funnel ogre-fearing parties his way for a light repast? How does that fit in with player agency? Does it preserve it because it was prewritten and not "fudged" and play time? Sure, they may have been tricked, but if they had spoken to Lefty LaFave at the bar, he'd have told them all about the notorious tricks of Carleton the Crafty Ogre, but they chose not to talk to him because he smelled like sweat socks that have spent too much time in a 13 year old boy's hamper.