... i've yet to see a modern digital epic look as good as a david lean film.
Isn't that more a testament to Lean, than anything else. Like you said, doesn't it depend more on the ability of the maker?
Plus it's a bit apples to oranges isn't it, David Lean adapting Charles Dickens' novels is less likely to need the type of special effects adapting Burrough's Barsoom novels would.
And Maybe it was wrong or unfair of me, but I wasn't expecting Lawrence of Arabia when I saw John Carter. I was hoping for something better than Green Lantern, or Cowboys & Aliens and what I saw was no worse or better than the last two live action Star Wars movies. But what do I know I liked the Dino De Laurentiis' Flash Gordon better than the last two live action SW movies. None of which were Lawrence of Arabia either, and I'm just guessing here but I'd bet no one expected them to be. “Sometimes you have to let art flow over you.”
Not that I wouldn't want to see an adaptation of Princess of Mars, that attempted to be near the quality of a David Lean film. I'm just not that hopeful.