You seem to be assuming that the Hatch/Wall Street Journal proposal would cover only federal courts; it covers state courts too. I think your redundancy argument w/r/t the federal courts alone is off base. Even if the Tenth Amendment weren’t there, I don’t think there’s anything in the Constitution that authorizes federal judges to demand same-sex marriage. But if the Fourteenth Amendment’s equal protection clause really did authorize that, the Tenth would not be a good reason for them to refrain from acting: the later amendment presumably supersedes the older in cases of conflict. The Hatch proposal would clarify that no, the federal courts cannot impose same-sex marriage on any constitutional theory (while also blocking state courts).