Something that you might want to consider as well: Azeroth has been in an almost constant state of war for the last 1000 years, with large scale conflicts going back another 10 000 atleast, with differing enemies using vastly differing tactics. As shown in WC3 and TFT, even when -their own dead- come back to life they can build new tactics and push back. The tactical abilities of the leaders of a group of soldiers under the Alliance would more than likely match any of those held by a Marine leader, so it really comes down to 'can 100 guns beat 5000 swords'.