I have seen a bad hire having instant impact on team and after person was let go, team was still getting back on track to pre-hire productivity for another 3 months.

We know all managers that say "stack doesn't matter, we can swap devs". We had C/C++ dev hired to do web dev with C# and Typescript.

Guy was utterly incompatible even if he was smart but management wanted someone who is local and can come to the office and that was this guy selling point.