But when judged as a payment method it has such poor usability that it seems pointless.

If you point out that it has poor usability for payment, well, it's actually a way to store your wealth. If you point out that the volatility makes it a bad idea there, well, it's actually a vehicle for speculation. Why would you speculate on randomly-generated numbers? Well, because it's so good for payment... or keeping your money away from the government... or... crap.

Bitcoin fills a niche that other payment methods can't. IMHO, that's the only value in it.

Bitcoin enthusiasts just have too high expectations for it.