Frankly, I do not see value in it, especially when it comes to things like history, geography etc. Even in math you do not need to be able to solve those super-hard triple star olympiad like exercises. You just need to be able to solve normal ones.

The only other option is that the weaker or average student will not even see those hard exercises exist and I not sure how would that help him.

That approach makes sense only if you mean to become expert in that subject. It does not make sense to demand that in everything.