Presuming that you are talking about the current financial system then that is just incorrect. Presuming that you are talking about some other cyptocurrency that nobody uses or supports, then, good luck with that line of thinking. There is no other (current) viable solution to the Byzantine generals problem, which is the primary reason that bitcoin (or any "cryptocurrency") has got anywhere. Without that, all other flavours of crypto are useless (unless build on top of bitcoin).
I am talking about decentralized vs centralized systems.
The cost for immutable transactions in any crypto-currencies is too high.
And we can not decrease it.
When the hashrate will stop growing it will be easy to collect old switched off asics, turn them on for an hour and gain 51%
Sorry. No way.