"The bookkeeping and storage is among all the network nodes" - can this system be corrupted (rhetorical question for there is no such system that cannot be corrupted)?I don't think you understand decetranlized cryptocurrency. Might be worth reading about it more.
The above IS NOT neccassery. Because the technology solves both problems and removes the Bank and the Money Transfer Agency.
The decentralized network is international and uncentralized. The bookkeeping and storage is among all the network nodes. The transfer is user-based and not orchestrated by banks or governments or controlled by them in any shape or form.
When system will get corrupted (for example using fraudulent transaction that will look legit) who will reimburse your loss then?