And if you also think what happened in Germany... It wasn't just berlin that got totally destroyed. Cities like Dresden or Köln, well, there wasn't much left of it after the allied planes passed. And i personally think the allied would bomb Jappan a lot more than they bombed berlin. So after Tokyo, probably every larger city would've been bombed by night carpetbombings and you aren't hitting a lot of fighting soldiers then...
According to wikipedia, (i kno, not the best source, but it can give an idea) 305 000-600 000 people died in Germany during airraids only, in Japan, 330 000 - 500 000 (nuclear bombs included)
in 7 months. I think this gives an idea how Japan would have looked like if those nukes wouldn't have fallen. And now, we're only talking about airraids, how much cities were shelled to by artillery? And ofc, how many soldiers on both sides would've died. I think Iwo Jima is a nice example of what would have probably happened. First, it's bombed to stoneage, then an enourmous amount of American soliders arrive and kill whatever they can fight, while being shot at from every possible place and being banzaied by japs who refuse to surrender and even till days after they got Suribayachi and the battle was over, they heard explosions every several minutes of Japs blowing themselves up to "save their honor". Also: when you plan a landing, you will need ships to cover the landing, with the increasing of kamikaze's and subs that were still active around Japan, that would've also costed some thousands of lifes. The russians were also planning to come to Japan, and we al know how much Stalin cared about a few thousand deaths more or less, as long as he got as much territory as possible
To conclude:
Speaks for itself i guess