[1] https://www.theguardian.com/world/2005/feb/01/iraq.suzannego...
There is another possibility on Xaya and I believe Ethereum has implemented as well now. On Xaya they are called game channels. The idea is that you allow a side branching chain to develop between an arbitrary number of people, then when a game is over you inject the end of the side chain back into the main chain and verify it. They invented it for near realtime verification between consenting parties, then you only pay the main transaction fee when you get back on the main block instead of very every action. But that type of system doesn't have to be only done with games obviously, that could be applied to anything.
If you are interested more in it, you can check this video out. They have lots of documentation and tutorials for the network as well.
Bitcoin doesn't care how much of it you have, as it uses Proof-of-Work not Proof-of-Stake. The only thing that matters is you computational power. Now it is true that large banks could just buy lots of ASICs and try to beat the network, but that would mean a continued investment: As soon as they stop mining, the network would return to normal.
They can hurt bitcoin (not that cheap anymore) by making it unusable for a period of time, but unless they are willing to keep mining until everybody else stops, they won't be able to kill it.
As far as usability goes i don't think bitcoin is that hard: Download an app, scan a QR-code, send money. Not that complicated. The transaction rate is a problem, though.
I agree that some people are too enthusiastic about crypto, but I think it still has its place. It doesn't have to kill banks.