Well, he is, in the same way that any country’s leader is ultimately responsible as in “The buck stops here”.
But there’s evidence that he wasn’t even told of the impeding attack. That the intelligence services of the IDF, its “Operations Branch”, did know, but that the leadership of the IDF did not believe -- or want to believe -- that anything would happen. And that therefore they instituted no preemptive measures.
Where do we know this? From a report, 5 October, by the Israeli TV Channel 12, as reported by Caroline Glick here. There’s more on the why’s and wherefores of the IDF failures.
How reliable is that? I don’t know, save what I read on Wikipedia about Channel 12, which seems to indicate that it’s pretty kosher, respected, and responsible.
So, in a choice between the views of some “cosmopolitan, secular, liberal” Moshav residents in Tel Aviv, or Channel 12, I’m going to go with Channel 12. Until something better.
IOW: it wasn’t Bibi that failed the intelligence test. It was his Generals, specifically the Hamas-friendly lefty ones.