If you keep chickens like some commercial operations do, debeak them, keep light low, automatic poop handling, and some other things that we normally don't do, you can keep a lot of chickens in a small space. We on this forum normally don't do things like that.
If you have a secure area and a climate and other conditions where all you use a coop for is a safe place for them to roost, where they always have access to a larger area to roam when they are awake, there is not really anything wrong with that size coop. You feed and water outside, manage the poop, and never leave them in there when they are awake. There area some people on this forum that do that and their chickens actually lead a real good life.
The problem I see is that people think they can leave that number of chickens locked in there and they will do OK. That is a problem.