"You conveniently assume that by not providing evidence as to the size of this figure, the plaintiffs, defendants and jury have valued it at zero."

It's irrelevant what they valued it at: no evidence means no damages. Period. Cases are dismissed every day for failing this fundamental requirement.

But, you say, there's a statute that presumes some level of damages. That's true. What's also true is that the statute authorizes punitive damages, lumped together with actual damages.

That's a problem under recent due process / punitive damages jurisprudence. Per the Campbell case, you cannot have punitive damages that grossly exceed the actual damages. Here, actual damages appear to be a single person's use of 30 songs, yet the jury awarded $675,000. There is, quite obviously, a large punitive element.

You are not in a position to argue these punitives were only a small fraction of the award, since, as noted above, actual damages proven were, at most, $30.

Your argument is that Congress can simply sweep these issues aside, lump them together in a statute, and be done with it.

That's not how constitutional law works.