My first run-in with Medium was with actual journalists (see: War is Boring whom have left Medium to their own site now). So while I understood there were many one-off blogs like mine that shouldn't be considered professional, many were and that lent any blog on the site some level of credibility.
Of course - all of that credibility was lost when a few bloggers were censored and kicked from the platform for wrongthink. I don't use Medium anymore.