> banks aren't too unhappy about the dampening effect it has on liquidity flows
Correct.
The average FedWire is $5.4mm [1]. The Fed Funds rate is 5.3% [2]. ACH settles in 1 to 3 business days [3]. Actual/360, that's $800 to 2,400 to finance wholesale.
If, on the other hand, you're JPMorgan and can pay 2 bps for deposits [4], that cost drops to $3 to 9. These are the economics that drive bank consolidation.