Man, how unfair. Horde can use this to completely bypass most of the Alliance defense! That's just as absurd as Alliance being able to use the hills near the Horde base to jump the fence.
Is there some proof that this could've been done during pre-nerf version of Alterac Valley? Maybe this area was laden with mines as well before the mines were removed. Additionally, the only videos that I found showing this exploit do not make mention of that specific hill which is far away from all of the action.
If you want to leave garbage exploits like this in the game, you might as well include all the other garbage exploits in the game from pre-1.12 versions.