Oh, there is no doubt that Genghis Khan directly caused the death of more people in his time, both in absolute number, and definitely as a proportion of the human population.
To compare the two, I would really recommend listening to the Hardcore History podcast series by Dan Carlin. Particularly the 5 episodes on Genghis Khan. Basically this is a perfect example of historical revisionism at play. We are so far away in time from Genghis Khan that we've become less sensitive to his actions. He wiped out entire cities (men, women, children, and even animals) as a natural part of his campaigns. Because historians of our time are so far removed from these atrocities, the 'grander', more large-scale effects tend shine through instead: his conquests, his facilitation of rules and measures, the Silk Road, trade with Europe, etc. We take a similar "Great Man" view with Alexander the Great and Julius Caesar. But really, at the end of the day, these are people who sought glory and conquest and who were no more than thugs who were better at killing people than the next person. They were not trying to make the world a better place.
Do you really think Genghis Khan killed 30 million people so he could create a universal monetary system and trade with Venice? Yea, doubt it. He did those things to increase control of his empire, and we're largely attributing the positive long-term effects to intent, though I'd say they were largely unintentional.
Adolf Hitler is different because we're only 2 generations removed from him. Many of us still directly
feel and remember the personal toll of his atrocities. It is difficult to examine him and his longer-term impacts on the world because it is difficult for us to disentangle our personal feelings and associations. Our impressions of Hitler today would be similar to contemporary impressions of Genghis Khan from, say, the Muslims that he conquered in the 1200s.
In 800 years, who knows. Perhaps people will look back on him as a catalyst that spurred massive technological innovation in space research and energy research.