>> It takes some financial assets 3-5 days to settle
That 1-5 days to settle isn't due to slow and disconnected systems though, which is what many looking from a tech perspective believe. Most financial transactions are matched in settlement systems the same day they are traded. The 3-5 days is for prefunding of underlying accounts, tear ups and other asset class idiosyncratic reasons.
What does it mean to fake a transaction?
What does it mean to verify a transaction? With Bitcoin it's possible to do because the balances are public. But once you start making transactions private that deal not in value that exists on chain, but are merely promises for some externally held value, then who can verify its legitimacy?
By providing a common ledger that can be used when you desire single entry bookkeeping you don't necessarily need all the backchecking as you're using a smart contract to ensure upfront that when the money is settled the assets move.