In Medium, this is actually better than mirroring the text from elsewhere in the article. The problem is, some people (including me, actually) use pull-quotes not as pull-quotes, but just as ordinary quotes or to emphasise a point.
In other words, the pull-quote is meant to be read linearly, in line with the ordinary text, as if it’s just another formatting like bold or italic.
So when I see a pull-quote, I need to decide: am I suppose to read this? Is it just a repeat of something stated earlier? Is it foreshadowing something that’s written further down? Or is actually part of the main body, meant to be read right now?
This only applies to Medium, though: I guess the formatting is a bit limited so people sometimes use ‘pull-quotes’ to increase their options.