It's the combination of the whole, including and especially the whitespace rhythms (which are still connected to font metrics, of course), that lead to the 1 page is approximately 1 minute guideline metric, because scene descriptions and actions have different whitespace from dialog.

Interestingly, compared to your expectation that a Tarantino screenplay would be more dense than the Fury Road screenplay, it is actually dialog that has a lot more whitespace overall in the screenplay format (they are subject to smaller inner columns) than scene descriptions/action descriptions (which use the full width of the page). Word count wise, action involves a lot more prose than dialog and many of the best action screenplays have more overall word count than a more dialog-heavy screenplay. (What I've seen of the Fury Road screenplay read like a novel, though as is pointed out elsewhere it is fascinating because it was written storyboard first, which is the exception rather than the rule.)

The screenplay format really is a fascinating thing to study. There are some great books out there on the screenplay format and how it came to be what it is today.