Does the matchmaker use SR averages only, or are there unspoken variables?

Weird and mathematical presumably means that it is a floating point number.

You say that I have confirmation bias, but your confirmation bias is to the point where you cannot understand the plain meaning of the text.

But here is another quote for you: “Anyway, this leads me to matchmaking rating…All the system does when it comes to matching on skill is attempt to match you with people of a similar number.” – Jeff Kaplan Overwatch Forums

But if you want all the quotes, see How Competitive Skill Rating Works (Season 15), references section.