Furthermore the article is self-contradictory, e.g. first it says the conventional bombings were so successful that a nuclear wasn't necessary, then it says since the conventional bombings were unsuccessful the nuclear strikes also wouldn't make a difference (pure conjecture by developers of the weapon, who are no experts in neither politics nor military strategy or history).
It's also simply a lie that the casualty estimates were pulled out of thin air. Ask yourself: don't you think the US army would try to estimate how many of its soldierd would die (cost) vs how many Japanese soldiers would die and how many military targets would be destroyed (benefit)? Of course they did a huge study on this topic!
The article also suggested the Japanese would've surrendered if key people had been left in power. Yeah, maybe (again conjecture). But for comparison: if the US had allowed Hitler to go unpunished, conquered territory to remain under Nazi possession, the Nazis would also maybe have surrendered earlier. But why would you even offer such a surrender? It would render the entire war pointless.
And from the Allied perspective, after the Bataan death march, the massacre of surrendered US troops and civilians in Wake, and the hundreds of similar massacres of surrendered allied troops, and rape and murder of nurses and civilians, across the Pacific, no one was going to allow the Japanese leadership or military off the hook.
That's begging the question - was a US invasion the only alternative? https://www.commondreams.org/views/2020/08/05/nuclear-war-or... argues that Japan would have surrendered without the bombings. And that's for unconditional surrender - a conditional one would be even more easily achievable.