And we already see, that Tarmon Gai'don will be quite similar to the biblical Armageddon. That means it will be really, really bad. We certainly didn't reach the worst part yet.

Ishy showed at his DF Social that the rivers will yet turn to blood and stars and the moon fall. With all the rotting food, one can expect that the DO's next logical step will be to turn the fountains, rivers, eventually all water into blood. Contrary to humans, the Shadowspawn will probably still be able to drink it (and maybe it will even allow Shadowspawn to cross such blood rivers).

Besides the horrible food problem, riots among the Lightside armies and the ghosts, especially plagues, earthquakes, volcanoes, floods, hail, fire & lightning storms, meteorites crashing down on the world, maybe a bloody moon and finally the darkening of the sun will happen. All this will of course kill many people and put terror in the remaining mankind.

Therefore I think the assumption that the Lightside will be able to organize a nice military campaign against the Shadow seems too optimistic and misses the point about what TG actually is. It's the possible end of the mankind. There will be desperate battles by a starving and tired mankind against the Shadowspawn hordes. They will need the Ogier, the wolves, the Heroes of the Horn and charismatic leaders to have a little chance to survive, but in the end only Rand can save them, if he defeats the DO.