Wait, are you saying that Thunderball - easily the worst Sean Connery Bond movie - is actually better than the book? Ive never read the book, but sounds like I shouldn't bother.
As an aside, during the Winter Storm I decided to watch Thunderball and its remake, Never Say Never Again, just to compare them. Thunderball is awful - noticeably bad editing, a crazy underwater battle with harpoon guns, etc. - but Never Say Never is kind of a joke.
It was made by Kevin McClory, who owned the film rights to Thunderball separate from Albert Broccoli, and its like a cheap, B movie version of Bond. Its only redeeming qualities are the return of Sean Connery to the role, and Kim Bassinger as Domino. And Mr. Bean plays a British Consolate in The Bahamas.