The issue is that the conditions must be the same for everyone for a competition to be fair. If I am less flexible and can't get down a steep slope as fast as someone else, have I the right to demand that such slopes be eliminated? Of course not!
but in the same way you could say that someone with better o-shoes has an unfair advantage over someone running in a pair of trainers for getting downa steep slope, because they have chosen to use equipment that makes it easier for themselves, very much like a visually impaired orienteer using a larger scale map.
i would expect that anyone could get a larger printed map for a race if you ask in advance (as mentioned above), so really i dont see what the problem is.