Citations, no.
Stats from my games, overwhelming (as I provided already above).
My experience, overwhelming.
Experiences of others, exists. For example, a fairly recent thread:
As for the difficulty mixing, it’s not a matter of being capable. As you pointed out, there’s no development on SC2 anymore. There is no staff. So nothing will be added to the game that could give the option.
As for the commander level capping bug, it’s also not a matter of being capable. Again, the game is not in development, meaning bugs are prioritized based off impact. Now, only the most severe/impactful bugs are fixed.
As expected. As already stated, they are interested in starting games the quickest, thus there has never been an option to specify one’s ally, even in all the years Coop existed and was being developed.
It’s not just Coop; it’s also Versus.
It’s not just SC2, it’s SC1, WC3, and D3, etc.
In other words, it’s been clear for decades that it’s Bliz’s philosophy to do this the way they do.