U.S. financial institutions ended yesterday significantly worse than the market overall ($XLF fell 10.77% while $SPY fell 9.64%) so I think that's prima facie evidence that it's wrong to view yesterday's Fed operation as distinctly benefiting the banks.
The government swapped one form of risk-free liabilities (central bank reserves) for another form of risk-free liabilities (Treasuries) because for market structure reasons there are reasons to prefer reserves.
As @NathanTankus pointed out, the left's takeaway shouldn't be "The Fed just gave $1.5 trillion to the banks, why can't they give $1.5 trillion to everyone else) but rather, the Fed just demonstrated that there's no fiscal constraint in DC, and so therefore spend more damn money!
When you see that $1.5 trillion dollars worth of reserves can be created and used to purchase Treasuries, with virtually no market impact to speak of, that should tell you how insane it is for anyone to think that we're running lower on fiscal firepower or anything like that.
