Yeah, OLCI is pretty nice because it allows you to lock in the room type and at least best location (I like corners, against stairwells, away from the road, and other quiet places). You can always negotiate with (beg) the desk for an upgrade the way you would have to anyhow at most Hilton properties. Hotels have been overselling in general and on room type since the dawn of time, but that doesn't make it right when a guest doesn't get what they signed up for. One can definitely push on this with management or corporate as needed.

However, once a compromise is accepted, generally all leverage is lost. OP mentioned that the guests accepted (well, it at least implies they accepted it) a discount. Was it to their liking? Do they consider the deal fair? OP doesn't explicitly state what they're looking for - it sound just like a curiosity since there is no ask about compensation, etc.