Unfortunately not. Financially motivated attackers are always going to find attack vectors, whether on-chain or off-chain. Blockchains can make things more auditable, more expensive to attack, and can eliminate some categories of fraud—but it does so at the expense of enabling entirely new categories of fraud.
On the whole, I do think the world is more secure in a post-blockchain world. But fraud will definitely still exist; the game will just evolve and become more sophisticated. (And possibly be pushed more off-chain.)