Exactly they are completely separate, reinforcements are what turned AV into a rush or die game not the removal of NPC’s.
Before reinforcements either side can do exactly what I 'm suggesting, stop being lazy and break the zerg and still win. Post reinforcements that is impossible for alliance to do which means alliance has to rush. But if horde play D alliance loses by default, when that started to happen alliance simply stopped queuing. And that’s where we are today, both sides simply zerg because there is no alternative.
That is 100% because of reinforcements.