1. Shut your mouth and listen, and
2. Divinity comes in some ugly forms.
The genius in East of Eden isn't in Steinbeck's willingness to bridge that fourth wall. It's a part of it, certainly. I doubt he was the first to write himself into the story and use it as the key to unlock his moral, but he was damn good at it. He usede himself unlike others, however. He used himself not as a fictional character, but as a fact.
It's not unlike Cal. He makes us distrust and dislike him at first. It's the only way we get to really love him. At least I do. He, Samuel and Lee are the only realized characters. Even Adam, for all his worth, is a surprise when he has a thought. Adam is a device, Cal is the character.