Okay, work with me on this one.
MARC is kinda like modern western tonal music. It provides a fairly strict structure but allows many ways to play around with what that structure really means. You can catalog (play) all kinds of materials (popular styles) with it. It's modal in that the same sets of tags and indicators and subfields can be essentially downshifted into other gears that provide different meanings and feel surprisingly different from each other (aeolian, mixolydian, phrygian), and only really skilled catalogers know how to make that work, but, still, most people can grasp how to describe books with a little training.
RDF is twelve-tone. It's mathematically rich and can be used to construct all manner of complex superstructures but when you get right down to it, there aren't really a lot of people composing in it today, so to speak. Sure, there are a few notable exceptions (Piggy Bank, Stravinsky), but how many of you spin the ol' Schoenberg on your iPods?
The rough-and-tumble world of Rolling Your Own Metadata Strategy is all about free jazz. Maybe you'll be lucky and find a few kindred spirits and together once in a while you'll find harmonies or a groove or a sharp, memorable dissonance worth sustaining. But it's unlikely to take off among the broader populace even if you have double your rhythm section. If it's your thing, you might as well name your next schema Ornette, since more of us should know that name, but don't count on the world beating a path to your door no matter how brilliant an innovator you might be.
Dublin Core is rock-n-roll, a usually (but not always) severe restriction of major-minor tonal music not unlike the pentatonic scale. Fifteen elements and the truth!
The manner of complexity inherent in the loosely interpretable notion of "catalog records" which the googles of the world present us with in our journeys to the Great Stacks is sugary pop music. Catchy, instantly recognizable, ultimately effective worldwide, but still just a surrogate for what we're really after, no matter how carefully crafted.
A stretch, to be sure. Never been one to spin out hit singles, me, but I'll keep trying.