To win in court, the farmers will have to convince SCOTUS to overturn
Wickard v. Filburn. Although I don't believe a Fifth Amendment "takings" argument against that precedent has ever been adjudicated by SCOTUS, for them to accept that line of attack against
Wickard would result in revolutionary change.
I can't believe the Justices don't know this. That's why their ruling mandating that the Ninth Circuit hear the case is fascinating.