This does not seem like a valid position.
It has nothing to do with whether or not they would have used them. The reason that it was better for the US to have them is because Nazi Germany was conquering sovereign countries through military action, not to mention engaging in the industrialized genocide of millions of people.
Their position rests on the fact that most people agree that the Allies were the "good guys" and the Axis were the "bad guys" in WW2, which is not a position that really has to be defended.
If Germany or Soviet Russia had the opportunity to use nuclear weapons to impose their will on their enemies, one need only look at what happened to the victims who already fell under their dominion.
But we do know for an absolute fact is that the US did use nuclear weapnos to kill thousands and thousands and thousands of innocent men, women and children (and for the sake of balance, we do know for an absolute fact that the Nazis did kill thousands and thousands and thousands of innocent men, women and children, but not using nuclear weapons)
There is only one country with actual blood on their hands here with regard to nuclear weapons - the other nuclear powers have so far been able to show restraint.
As such, I find it pretty objectionable for people to suggest that it was "far better" this way, when the evidence really does not back it up.
I am not saying it is not best possible outcome for the world. Could it have been worse if the Nazis had for example nuked London in 1945 and killed a million? Sure, of course that might have happened, but it didn't actually happen. Perhaps had the nazis had that chance, the UK would have surrendered and there would have been peace and countless lives could have been saved and a completely new era of peace and prosperity begun? Or perhaps it would have also been untold slaughter and misery like the US did to Japan?
We just cant know, and so I object to people saying it was "far better" for history to have played out the way it did based mainly on - I suspect - the plot of Hollywood movies they've seen. History is written by the victors.
Anyway, this is way off topic and Godwin's Law has clearly been invoked. We should stop.
Regardless, the atom bombs were certainly not the worst things any country did in WWII. The US firebombing was far worse. Everyone did bad things in that war.
Stop using your modern sensibilities to judge them.
Secondly, your assertion that we can't know what Nazi Germany would have done with nuclear weapons is correct, but you seem to be interpreting that as meaning "all possible outcomes of Nazi Germany having nuclear weapons are equally as likely", which is absolutely not true and a common mistake to make in an argument.