I have two primary issues with Medium:

1) It's essentially halo-effect-as-a-service. People assume that since it's on Medium, it'll be a high-quality of work, but more often than not, Medium posts lie on the pseudo part of pseudointellectual. Which leads into...

2) Complete lack of any personal branding. Not even a username in the URL. Yes, it keeps things simple, but it dramatically reduces the personal benefit from posting on Medium. Even worse, in line with the previous bullet point, the lack of branding leads writers to spam links to their Twitters with the cliche "if you liked this, follow me on Twitter!" And recently, I've seen people say in bolded text "PLEASE CLICK RECOMMEND." It's jarring.