.

A crossbow and heavy armor are incompatible.

Think what you want, but I know for sure that there was even a special hook on the armor to make it more convenient to shoot. And in general, all these highly praised elven arrows and bows are nonsense. Firstly, elves are not professionals in this field. They can only make bows that are suitable for hunting. Secondly, even to pierce chainmail, you need a sharp iron tip. I doubt they can make something like that while sitting in trees and eating bananas.
Another thing: a bunch of pointy-eared idiots, entrenched in the forest, will not be able to withstand an entire army, even if they are initially lucky and use the element of surprise and maybe even injure someone, but they will quickly be found and then put on display for everyone to see.