You can imagine a successful financial system without a stock market if you don't know much about financial systems, in the same way that you can imagine a jet flying without wings if you don't know much about aerodynamics.

I believe that the rise of importance of finance has been a net good for humanity, but I know that's an unpopular opinion and I've seen good arguments that it's a net harm. But I don't think you can make a reasonable argument that we could have a modern world anything like the current one without stock markets. Banks and credit unions don't, can't and shouldn't provide the kind of funding that equity markets do.