It’s hard not to look at his departure through a cynical lens. He’s not been supportive of other critics, both from and outside of Google. He also wants to use his history to (rightfully) claim expertise and power but not to offer solutions.
I disagree. My read on him is that until very recently (i.e., possibly when GPT4 came out) he didn't take x-risks concerns seriously, or at least assumed we were still many decades away from the point where we need to worry about them.
But the abilities of the latest crop of LLMs changed his mind. And he very publicly admitted he had been wrong, which should be applauded, even if you think it took him far too long.
By quitting and saying it was because of his worries he sent a strong message. I agree it is unlikely he'll make any contributions to technical alignment, but just having such an eminent figure publicly take these issues seriously can have a strong impact.