Is it "arcane", meaning "understood only by a few" or "requiring secret or mysterious knowledge to understand"? No more than any other part of the Constitution. Is it archaic? Arguably, but I don't think that's a knock-down, drag-out case, either.
I would say it’s extremely vague and the reactionary courts have so misconstrued it, that no one really knows what it means anymore.That's the common progressive talking point on it, yeah, but I don't actually believe that it's true. Just because it doesn't appear to mean what most American left-liberals would like it to mean doesn't mean its apparent meaning is some great mystery.
Also the archaic part is covered by it being clearly antiquated, and meant for the 18th and 19th Centuries, not modern society.
Again, this is the standard progressive talking point, but I'm not sure whether or not I'm convinced by it.