I’ve almost never seen this job switch in a company work, but I’ve almost never seen it attempted. I have seen it work many times between companies. Everyone who switches careers does it.
I think there’s a hang up around “incompetence”. Maybe it’s something inherent to the person, but you don’t have much evidence for that. The evidence is the person/job pair. So, switch up the job if the person seems good.
Sometimes when I’ve struggled with a role that doesn’t feel right and I start blaming myself I think “Not everyone can do this. What if some super smart, healthy, well adjusted person was in this role but was this bad at it. What would he do?” I imagine some baseball player, marketing genius, or renowned writer and that he ended up in this job instead of that one. I guess he’d leave? I’ve actually struggled to come up with an answer but it feels important.