If you create a brand new channel on Medium or personal blog, then the later will find it harder to rank due to a low Domain Authority. In that case, your Medium channel has a higher potential to drive new traffic to the page.
However, when talking about Medium vs platform with established reputation and high DA, Medium will always be outranked. As such, when may today seem like a wrong decision (publishing on a personal blog) may help you rank better in the future if you continue to improve the strength of your website and your on-page SEO.