Absent a time machine, how could a hire in January have been working to clean up this mess "months ago"?

Blame the CEO and the rest of the management team for not hiring a good HR person sooner if you want, but I don't see how you fault the person who just walked into this mess. Unless you're blaming them for not seeing the mess or walking into it with their eyes open. To me, that seems counterproductive. Having people with the appropriate skills take on the difficult work of improving these cultures is part of how things get better.