You cannot take Spanish accounts at face value.

Why not? The most accurate accounts of an event are generally recorded by the people closest to the event at a given time.

They tend to have embellished many of the details concerning their actions and the actions of the Aztecs to justify their conquest.

They didn't need to justify their conquest. You're thinking with a 21st century mentality about people who lived in the 15 century. Sure shaped things to make themselves look better but every winner does that. That's just part of history. There's no such thing as 100% true history.

One of those embellishments is the scale of sacrifice the Spanish reportedly occurred. We don't have the evidence to support the numbers

Scale is always embellished to some degree. So? When your making pillars out of the skulls of women and children you've murdered then you're in the business of making pillars out of the skulls of women and children. Exactly how many were murdered really doesn't matter compared to the general practice.