It's sort of a constructive proof that you don't need crypto currency, if that's the justification for its existence.
3-5 days is actually a feature of ACH. This delay includes the ability to reverse a transaction, a built-in risk management. For example, here is a quote from an article on the front page of HN right now (#5, SIM swap horror story):
> After a couple of days, our bank reversed the $25,000 charge and told us that the fraud department caught the ACH withdrawal before it was fully processed so that neither my family nor the bank lost this money forever.
Google will give you lots of good information on the difference between wire and ACH.
It's a mainframe batch-processing system built in the 1970s, and it's mostly worked just fine for 40 years. That's pretty efficient!