This is great until a small time artist gets put on trial facing 10 years for art used by megacorp, that is originally theirs but hard to prove it.

In this scenario, has megacorp proved the art is theirs? Because, if so, how, and if not, then surely the original claim isn't unambiguously fraudulent?

How do I prove it's fraudulent? Hire a lawyer?

Crimes are prosecuted by the government.

Never denied this fact.

To be clear, I am suggesting that fraudulent DMCA claims should be a crime, the government should investigate and prosecute these claims after you report the crime to them.