Writing about sacrifice at this site means keeping three questions apart, because they are routinely collapsed into one and they have three different answers.
The first is whether it happened. Here the site answers plainly and in its own voice. Human remains are present in dated, stratified offerings, some of them decapitated crania, some of them children associated with the shrine of the rain god. None of this depends on a Spaniard having written anything down. The excavated deposits are the evidence, and the practice is attested.
The second is at what scale. Here the site answers much less, and honestly so. An offering cache tells you what was placed in it, not how often anything happened across a century in a city of that size. The totals that circulate come from colonial-era narratives, and the arithmetic in them is not arithmetic that anyone performed. Modern estimates differ by more than an order of magnitude, and that spread is a real state of knowledge rather than a failure to look it up.
The third is whether the source that tells you is trustworthy, and this question has to be asked separately of each source. A conquistador writing a justification of his own campaign, a friar compiling testimony from Nahua informants a generation after the conquest under Church supervision, and a stratified deposit under a colonial street are three different kinds of witness with three different failure modes. Treating them as one body called the sources is how a figure invented in a polemic ends up quoted as a measurement.