but because the top of the barracks offers a great position for attacking any vehicles that might be in the entrance and those that drive up the ramp in the middle of the base.
A position you shouldn't have.
Same with getting on top of the mountains around the canyon, that gives you a great spot to attack and defend from... But why is it inaccessible unless you exploit bugs?
Because it wasn't intended, so logically you shouldn't allow the Barracks exploit either. All in the interests of fairness.