Combat we were actually discussing on a scenario of genoside not conquest. Wouldn't those factions defend themselves in a case of genoside by any of those two factions? Let's be honest. If you were Tirion and suddenly one day Garrosh decided that you and everyone on your faction will be destroyed along with the Alliance in order for the Horde to reign supreme what would you do? And yes you are right Combat about the Demon Chain but still that doesn't make it an unbeatable Super weapon. Garrosh could indeed get more proto drakes or Magnataur from Northrend but he didn't. We are talking about a possible scenario that would happen with what we have right now and not what we could have cause in a possible all out war the Alliance could also have equivalent means of defence in those things. Noone really knows what those Anima Golems can do. What we know is that the Focusing Iris have tremendous powers on the right hands in the right place. I never overestimate the Iris. I just mention what I know from the story and the potential of the weapon. The Powers of the Thunder king is not a measly lightning enchant. Noone knows what Jaina gained when she gained his powers. Only the developers might know. The only source I have for the Alliance population and the % that they have in their army is mostly the RPG Books. I know that you may say that they are not canon but unless we have something better I prefer to follow it than nothing.
The story has some similarities and some differences from the second war but the same result. The Horde was bound to lose the war just like in the second war because they have different races with different ideals. They would never be United in a genoside scenario as their ideals are different.