IT might be 1/4 as much security, but, at least for that first confirmation, you can at least see that it had valid inputs. That is worlds more security than accepting a zero confirmation transaction.
Are you implying that that there is a requirement for a miner's confirmation to verify valid inputs? Any node can (and does, all day, every day) verify inputs before relaying the transaction. There is absolutely no reason to wait for a block to be mined if all you're concerned about is verifying inputs.