He's right that Bitcoin (and generally, cryptos) do not serve any mainstream purpose outside of speculation.
Besides investing in bitcoin, I am still using bitcoin to transfer money and make payments to some overseas customers and services, so is he correct in saying that bitcoin is only used for speculative purposes?
No, he's saying it is not used for
mainstream purposes, e.g. replacing everyday credit card and cash transactions for instance. After 14 years and hundreds of billions of dollars, Bitcoin processes perhaps 0.00001% of the world's transactions on a daily basis.
Blockchain is a great architecture for what it was designed to do, but the problem it was trying to solve is
very narrow.
The current system where every user is a network node is not the intended configuration for large scale. That would be like every Usenet user runs their own NNTP server. The design supports letting users just be users. The more burden it is to run a node, the fewer nodes there will be. Those few nodes will be big server farms. The rest will be client nodes that only do transactions and don't generate.
See? He used even those words: "large scale". And also "big server farms". If he didn't think about mainstream, why he used words like that?
His idea of "large scale" here was
thousands of users, not billions. If you told Satoshi that he designed a system that would replace the world's daily credit card transactions he'd say you were out of your mind.
Satoshi wasn't a moron, and he knew very well that blockchain would never scale to anything close to mainstream.
Simplified Payment Verification is for lightweight client-only users who only do transactions and don't generate and don't participate in the node network. They wouldn't need to download blocks, just the hash chain, which is currently about 2MB and very quick to verify (less than a second to verify the whole chain). If the network becomes very large, like over 100,000 nodes, this is what we'll use to allow common users to do transactions without being full blown nodes. At that stage, most users should start running client-only software and only the specialist server farms keep running full network nodes, kind of like how the usenet network has consolidated.
So, is it "a lot of people", when you think about "over 100,000 nodes"? And again, there are "the specialist server farms" mentioned.
Nodes are not users. The network cannot process mainstream loads no matter how many nodes are on it.
Eventually at most only 21 million coins for 6.8 billion people in the world if it really gets huge.
See? When typing "for 6.8 billion people" of course he thought only about a small niche.