Imposter syndrome such a popular thing to belive in because actually most people really do suck at their jobs. I see a similar sentiment all the time where people say things along the lines of "Nobody really feels like an adult, we are all just muddling through" etc etc. Actually no, some of us actually have our shit sorted out and are actual adults.
Most people who I have encountered that are really really bad at their job do not suffer from impostor syndrome, because the whole point of impostor syndrome is that you are open to your own vulnerability and your own incompetence.
The people that are exceedingly and amazingly bad at their jobs are often bad because they refuse to learn, because they don't feel they need to. They don't practice humility, they don't ask open questions to learn and they don't improve their processes over time.
So while it's easy to kick in an open door and say "everybody can't be smart so some 'impostors' must actually be bad at their jobs" I think it's more useful to take a step back and try to focus on what behaviors and mindsets lead to development and growth, and which do not. I strongly believe that having impostor syndrome rarely correlates with refusing to learn due to one being convinced of one's own brilliance.