You have valid points. But look at the messaging. Great reviews, no raises, then "here, train your replacement" followed piping him to /dev/null. This isn't a recoverable situation. He's been had.
Considering how nobody is lifting a finger to help him, I reckon nobody else particularly enjoyed having him around, but couldn't get rid of him because of their reliance on his technical prowess.
It sounds like they're managing him out and he'll soon be on a PIP.