This seems like a good argument for adjusting copyright law, but seems unhelpful in interpreting it. "This law isn't a good way to achieve the government's objectives" is not the same as "this law wasn't broken". Judges do have some discretionary power in interpretation and that can take into account congress's intent, but here that would be a massive stretch. A judge would simply say it's congress's job to fix copyright if it's not the best way to achieve certain policy goals.
As I said, exceptionally hard in practical terms - just not as baffling as the parent poster painted it. With the right judge anything is possible, and US history is full of controversial "overreaching" judgements.
(and with the deep pockets GH/MS have, it doesn't really matter if the case eventually loses on a big principle - it's just a case of dragging it long enough that, some time through the whole process of appeals, the plaintiff will get broke enough to give up or accept a deal. This line is likely just one of many that defendants will employ.)
