Casino Royale is no doubt a Top5 of the franchise but the template came from the only original novel Eon had not adapted from the Fleming Novels. But I don't agree that Daniel Craig is the definitive Bond, but I guess it depends if you are talking about the one defined by the by the novels or the one defined by the movies, and I think most people's yardstick is the movies.
There is nothing wrong with taking Bond to grounded gritty spy thriller, the franchise has history in From Russia and Eyes Only, but for me the Bond movie template is larger-than-life stories, characters and villains, and Bond himself is more of a superhero than gritty, troubled, jaded spy. It's accepted that Moonraker and Die Another Day went too far into fantasy, which was what prompted the following films to go back to basics. In fact Daylights was a similar move following View to a Kill.
At the time Casino Royale was put into production there was no need to subseqently go grounded, Bourne and MI and others were seen as threats, but neither were as successful as DAD at the time, and I never saw the need to try and make Bond into something else as a result. Casino Royale aside, I think all the Craig films have been poor, and I don;t think Craig as Bond gets anywhere near being the best Bond across his body of work in comparison to any of the other actors, including Lazenby.
My favourite has been Brosnan, although I get your comment about his reign. But I remember so many moments in the Brosnan films that were definitive Bond, the nonchalant flick of the head as as bullets splintered the bookcase he was sheltering behind, the vodka drinking scene waiting for the assassin, the beating up of several bouncers behind the blackened window, and simple adjusting of tie, amongst many others. I do not have in memory a single Bondian moment in any of the Craig films. And Skyfall is full of things I hate, not least of which Bond quits in a huff, and ultimately fails the mission. This is not Bond.