>You find a high DA site that allows user generated content to be added and indexed. (the host)
>Common parasites include Medium, Amazon s3, Github, Linkedin, Quora, Youtube, ect.
Google rank does not apply to subdomains. The subdomain does not inherit any of the rank of the parent. That is why blogspot and s3 will never work in this regard.
Parasite SEO boost only works if the link passes ranking, the page itself has a lot of SEO authority, and there are not too many outgoing links. Medium will not work for this reason unless you get your link on a very high ranking medium page. Just posting your link on a new medium blog is useless. Same for Github, Quora, Youtube, linkedin for these reasons.