I am not sure if the comparison to "chazakah" is fair in the case of a mohel. Suppose a mohel performed 10,000 brisim without any baby getting herpes before one baby gets it. He then goes another 10,000 brisim until he has a second episode years later. I do not think that this would constitute a chazakah. The model that you give is the case of where two consecutive babies died after bris, and I believe no babies before that, I think that the case of the mohel would be much different.
In addition, we have a known fact that some families have bleeding disorders that are genetic and potentially dangerous. It is not a known fact that a mohel can transmit herpes.
I think that we generally agree on the whole matter. My point of contention is in the one limited limited case of one mohel associated with two cases where viral culture testing comes up negative. You have invoked a principal of chazakah. I am just questioning this one limiting case.
What do you think?