specifically, this:
http://www.calmecacanahuac.com/blog/uncategorized/ometeotl-the-god-that-didnt-exist/
Which would basically throw the entire understanding of the religion for decades into the garbage can.
I cannot however take it as face value because blogs like this do get things wrong a lot. Is there actual historical evidence that the supreme god of the Aztec Pantheon even existed to the precontact Aztecs?
I've read the blog post, and by the standard of blog posts, its pretty well sourced. It mentions the important academics, such as Miguel Leon-Portilla, James Maffie, and Richard Haley and it references their work so you can follow up on it. Most historians are familiar with their work, and they are reputable historical sources. It does lack a bibliography, but its a blog, so I'm not going to be too hard on that.
I'm not sure I really have much to add to its argument. However, this blog is not the only place where some of Leon-Portilla's interpretations have been critiqued. In 'The Allure of Nezahualcoyotl,' Jongsoo Lee spends several chapters dissecting Leon-Portilla's interpretation of Aztec poetry. This is only tangentially related to the question of Ometeotl's existence, but it might help give you some more background on these kinds of debates. The text also challenges the existence of Nezahualcoyotl's 'unknown god' which is also related to Ometeotl's reality, so the text may be worth checking out for that.
Lee, Jongsoo, The Allure of Nezahualcoyotl: Pre-Hispanic History, Religion, and Nahua Poetics, (Albuquerque: University of New Mexico Press, 2008)