In terms of padding, though, it's hard to beat Miguel de Cervantes. In Don Quixote, there is a section where the title character goes to a bar and finds a book. The bartender tells him that it's a novel someone left there, and it's pretty good, and he should check it out. So he does. Cervantes includes this (short) novel in its entirety, and it has nothing at all to do with the story of Don Quixote. It reads like Cervantes inserted an unrelated story into his manuscript in order to meet his word count.
Shakespeare also tries to kill time in Hamlet, coming up with excuse after excuse as to why Hamlet doesn't just get his revenge already, until finally he gets to the end of the play, and everything wraps up quickly in a contrived duel that Hamlet doesn't even initiate. The play is too long and the plotting is fairly lazy.
Moby-Dick, Don Quixote, and Hamlet are all flawed, sloppy in places, and seem like they could have used more editing. They have one other thing in common: they are three of the greatest books ever written. More than that, they are three of the greatest achievements of humankind.
Masterpieces aren't perfect. They're idiosyncratic, reflecting the quirks and obsessions of their authors. There are thousands of polished, technically proficient writers who have labored their whole lives and never produced anything half as interesting as Moby-Dick. At the end of the day, who cares if the point of view is inconsistent? Rookies in a creative writing class can give you consistent point of view, but they can't change the way you think about the world.
Which is why it baffles me when people dismiss Jack Kirby's work--the New Gods, for instance--because of his scripting. Yes, Kirby had a quirky writing style. He bolded words for no discernible reason, he used excessive quotation marks, and his dialogue is often awkward. There are countless creators who could write smoother, more readable prose than Jack Kirby. But none of them redefined the nature of comics storytelling like Kirby did. Kirby worked for years, polishing his approach, drawing stories with maximum energy and visual impact. He was better at composing a comics panel than anyone else who ever lived. With the New Gods, he created "An Epic for Our Times." When you consider those achievements, who cares about some oddly placed quotation marks?