Yeah, I agree it's probably the best heuristic (so far), but I would quibble with calling it 'great'. It's perfectly fine for estimating a user's reputation; but clearly, a set of followers is sorely lacking on its own for determining the reputation of a product, merchant, etc (when reputation really matters, IMO)... it's just that an npub-linked reputation of such things won't be particularly relevant until having their own npubs becomes much more relevant (or maybe that's a chicken-and-egg thing)