i don't think 100,000 Dothraki is unrealistic at all. It is a number that had been cited several times in the show, and is even used as the official figure in the GOT and ASOIAF wikis. True, that number probably went down a little during the Battle of the Blackwater Rush, but not enough to bring it low enough to the numbers you're speaking.

You are right though that the Unsullied numbers have definitely gone down, but I would say not below 6,000.

You are also right about Renly. Totally forgot about his force there. This may not be the biggest army in Westeros then, but it could definitely be the biggest battle by having 100,000 vs 100,000.

Fair, my number may not be as high for the Dornish/Ironborn/Martell forces, but Denaerys still needed ships to ferry her Dothraki to the Blackwater Rush fast enough to catch the loot train, meaning a large fleet must still be manned and existing.

Logistics would be a nightmare, Dany and Jon realize that this is their final stand and must put everything into it. The Nigjt King doesn't have to worry about logistics. He doesn't have to worry about feeding his army, maintaining his supply lines, or troop replenishment. No matter how many wights he may lose, he still gains troops from whatever living soldiers he kills. To the Night King, victory is basically assured to him, on top of having a zombie dragon that is faster and stronger than the living. He could wait out the living and let them starve, but why? His victory will happen, and the sooner it happens, the better.