His argument, in an extremely simplified form, is that the demography and archaeology do not in any way support tens of thousands of yearly sacrifices, and that those numbers come entirely from secondhand colonial sources who have an extremely obvious interest in painting their enemies as bloodthirsty monsters. I found it extremely convincing, but I'm not a historian.
What do historians think?
Here is an answer by u/400-Rabbits on this claim. The answers linked at the end go into more detail as well.