Capablanca was speaking in a time when openings were inaccurate.
Now that computers have come around and openings have been hammered and fine-tuned, going out of book can sometimes be an instant loss.
Quite the opposite. Going out of the book against players which are parroting computer lines is incredibly effective. Actually this method works even on the highest level- see how Carlsen is treating the opening.
The endgame technique of today's elite players is incredible. Yes, I'm sure someone will post a blunder, or a failure to win a won game by an elite grandmaster. But taken as a whole, the technique of world class players now is miles ahead of what Capablanca and his peers knew.
Capablanca's point about opening books may actually be right because most opening books are obsolete within weeks of being published!