I don’t think you are reading my replies because I clearly said: “While my experiences aren’t in line with their [Google] statement.” Therefore, I 100% agree, through my own experiences, that Google ranks subdomains differently.
However, those are only yours and my (and several others) experiences. I have spoken with others that have fabulous results using subdomains (including HubSpot). Since Google clearly and publically states the opposite of our experience, there is no way you can definitively say “Google interprets content off your primary domain as a poor user experience.” You can say it is your experience and disagree with Google’s statement (like I do), but you can’t say it definitively. If you could, HubSpot’s blog posts wouldn’t be showing up in the top search results and no-one would ever use a subdomain.
If I am working with a client that is a HubSpot customer and never had a blog, I would have no problem using HS’s CMS on a subdomain (in fact, we are doing this now). However, I would not risk the move of a client’s blog that is getting 100’s or 1000’s of organic sessions a day because of my experiences and not wanting to break anything (we do this most of the time).