What is the disadvantage of writing more of a shorter 'teaser' story on medium to funnel traffic to your blog?
Is that what you do with twitter and and reddit (funnel to medium)?
Either way, for me, the benefits of anything that makes content creation easier way outweigh the possible SEO penalty, so I don't really care.
I don't see the point of writing teaser stories on medium, I doubt they'll get accepted into big publications, or bring you a lot of traffic. For me, Medium articles are meant to close email subscribers, and the future emails I send can direct people to my site.
I've got started on twitter only recently, I post there for fun, writing practice, and sometimes I just share links to whatever project or post I want to promote.
Posts submitted to subreddits link to my main site.
I don't usually bother to manually promote medium posts anywhere other than submitting them to publications (because I might as well promote the main site).