I think you've misinterpreted what Bitcoin's "job" is. Although the initial impetus was definitely to set up a new type of currency (something I'd agree it fails at) it has long since moved to behaving as a store of value, or a commodity. At this it excels.

The tradeoff GP is referring to is efficiency for security. If you have a distributed, "trustless" network you unfortunately have to trade your efficiency for more security.