> how do you think lobbying Congress would even hypothetically help YouTube in court
With regard to Megaupload, this much is simple. The Justice Department can freeze an investigation under pressure from Congress. Whether an investigation comes to its conclusion or not is strongly under the influence of Congress.
YouTube was found to be in compliance with DMCA in federal court due to Viacom's case years before the DOJ bought a case against Megaupload. I don't know why YouTube would be worried about DOJ investigating something they had case law to support them on.
With regard to Megaupload, this much is simple. The Justice Department can freeze an investigation under pressure from Congress. Whether an investigation comes to its conclusion or not is strongly under the influence of Congress.