The final plan for Olympic called for 18 US divisions to attack 11 Japanese divisions. Don’t know about comparative size of the divisions.
I’ve seen claims the Japanese had 900,000 men on Kyushu by August.
The Japanese had plenty of men, but very limited stocks of fuel, equipment, ammo, etc. and almost no way to replace those stocks when used. Their combat power was not at all proportionate to their numbers.
Who knows what would have happened? What is very nearly certain is that the total number of casualties would have exceeded those of the A-bombs by at least an order of magnitude.
http://www.ww2pacific.com/downfall.html
If the Emperor had said to fight to the last man, woman, an child, they would have. We weren’t facing just uniformed soldiers. That said, they had withheld their Army and air power to meet us in Japan. We were facing an enemy that by our own estimates would have caused us at least 1 million dead and wounded. Truman (Not my favorite person by any stretch) knew this and authorized nuclear weapons. For all that I have read, he only did so after reading the military estimations, which we now know were reasonably accurate but still on the light side of Japanese capabilities.
I have one simple view of war: War is about obliterating the enemy or forcing an unconditional surrender. Nothing less is war. If you don’t like war, then don’t wage war.
Japan was attacking everything within its reach at the time. We were just another target destined to be attacked since there was no way we would have given in to their demands at the time or perhaps the demands they had been making in the region sometime in our future.