Of course, you're correct that the two cannot be compared. However, the statistical anomaly of the Mongol conquests were still far greater even considering the context. I have done the calculation before - it would be the equivalent of 1 billion people dying across Europe and Asia today. Do not underestimate just how devastating the Mongols followed in short order by Black Death (which was largely their doing) was.
That said, they cannot be compared, and the Holocaust is without doubt more evil.
Of course, in an ideal world mongol conquests can actually be considered genocide, and black death did follow on their heels thanks to their doing... Interesting that you actually made the calculation, I did not expect that! :)
And I want to add, if you are interested in history (looks like you are), there's some brilliant documentaries of world wars by BBC. Authentic black and white footage as well. Worth watching!