But your assertion was that banking is an "industr[y] that require[s] a large amount of startup capital" such that it will "lead to natural monopolies or duopolies." The fact that you can have a small, profitable bank disproves that.
Capital is more than just money. It takes a lot to jump through the regulatory hoops, money requirements, and insurance costs while having competitive prices against other Banks and still make a profit.
Even if it was just a money issue, new banks do still require a fair amount of money for relatively little profit in an industry that is well established. If someone is going to put their capital on the line, why wouldn't they put it in a higher growth industry?
These don't make new bank creation impossible, just unlikely.
In the same thread you state "Nah, it's just the nature of capitalism. Industries that require a large amount of startup capital lead to natural monopolies or duopolies" as the cause of centralization of the banks. Then you go on and explain where the high-capital cost actually comes from:
"It takes a lot to jump through the regulatory hoops, money requirements, and insurance costs while having competitive prices against other Banks and still make a profit."
I'm not blaming capitalism, just pointing out that in some industries, monopolies naturally form. If anything, I'm blaming the government for getting taken over by the rich instead of keeping the imbalances in line.