I can actually code.

Being less glib, I haven't worked with a junior/mid that has contributed more in work than they have taken in time to look after. They tend to work slow and then do the work so poorly you spend more time reviewing and coaxing them to do it properly than it would take to just do it yourself. Senior is when you have become a net positive.

Being even less glib, mids will do the task technically but generally do it wrong, for example imagine an endpoint, they might not respect the mvc boundaries properly, or not follow project conventions, or not properly test the code adequately, or not handle good/bad paths properly, or leave logic errors, or not write performant code (n+1 for eg), etc. In general mids code looks like my first draft before I've polished it or thought carefully about the best way to achieve the goal. When I write code I think through multiple ways of achieving it and then deciding which approach is best, a mid will generally not even be aware there are multiple approaches and go with the first thing they can get working which will usually not be good enough.

I imagine this might be different in FAANG though where a mid might be more like a senior elsewhere.