Evolutionary Atheists: Excessive Extinction of Survivable Mutations, your thoughts?

The theory of Excessive Extinction of Survivable Mutations argues that there is not enough surviving steps in the supposed evolutionary advancements of the human race. The logic of the challenge is that, if humans evolved to be as complex as they are, millions of mutations must have occurred. Any weaker mutations that did not die on their own, would need to have been exterminated. These exterminations would have either been by a catastrophic event, or led by humans. However, internal mutations would have been difficult if not impossible to detect without sufficient medical equipment, and therefore would have likely gone without being exterminated by any human-led efforts. Therefore today we would have many different variations of humans, and medical doctors would have to learn how to treat all kinds of human variations, some with different layouts of organs, some with or without certain organs or glands, etc. In fact, humanity today should look a lot like the bar scene in Star Wars. And yet despite the innumerable variations in skin color and facial/body appearance of humans today, the overall makeup and functionality of humans today is remarkably singular. If global man-made exterminations did not occur, then a catastrophic event would have been required to erase all survivable mutations. This event would need to have been fairly recent, as we have not seen any "new" alternate variations of humans anywhere that have come up since. And, it would need to have been a remarkably selective catastrophe, since it managed to wipe out every single variation of human except for minor racial variations we see today, yet it was not powerful enough to kill the millions of animals and bugs and birds and every sort of creeping crawling things alive today. If Lady Bugs survived, why didn't alternate variations of humans survive?