It's worse than fiat, but that isn't an alternative if you're a North Korean hacker, a ransomware artist, or an international drug dealer. Crypto does well at facilitating these use cases.
If cash is banned and a central bank gets the funny idea of setting the short term negative interest rate to -5% permanently, then corruption would disappear because the return on money obtained via corruption is no longer guaranteed to be positive unless it helps the economy more than the initial corruption damaged it. A few years later cash with demurrage fees would be implemented.
The day cash is banned, it's completely over.