...Regardless of that, it's at the core of blockchain technology that it can't do many transactions per second. It's not only bitcoin, it's blockchain in general that's unsuitable for payment systems.
That's pretty flawed statement. Cryptos are alredy proven to work as a payment system, because you can pay with them. What you're saying is
one blockchain/crypto is unsuitable to become a one, global currency. But, even assuming it's true, I seriously fail to see how does that makes cryptos worthless. Where did you get the idea "it's all or nothing"? Explain why Bitcoin, or any other crypto, is only worth something when it has the capacity to service every person in the world? Why would it have no value if stays forever in a niche?