How does velocity of money in gold and between central banks compare to the velocity of money with PayPal and Visa, either in volume or transactional bandwidth?
I don't think that there is much day-to-day traffic in gold between central banks because that role was fully devolved to the US$ in 1971. So, in the modern era there is a split between SoV and payments, which didn't exist before the 20th Century.
Bitcoin is a difficult comparison because it straddles and rejoins the two domains: currency and payments, so while gold is primarily a SoV currency, Visa is 100% a payment system and contributes to the velocity in fiat. The potential for Bitcoin is phenomenal because it can usurp both domains if computing technology permits. This is probably only a question of time because computing tech is getting more powerful at a much faster rate than the world economy is growing.
Bitcoin is also interesting because for the first time there is a currency for which velocity can be exactly measured, as most of the time it is statistical guesswork.
They are not incorrect about it won't run decentralized.
The most important single feature of Bitcoin is its 21 million cap. Decentralization is the horse for this cart. The goal is to maintain the 21 million (preventing extra issuance and double-spending). Decentralization is the only way to be sure of this, compared to say, XRP, which could be upped at any time.
The solution to centralization concerns is to implement payment channels for node services, as Justus Ranvier has detailed, not to restrict volumes by pretending that Bitcoin is competing with gold only.
