Without an Ephemeron, RDM sets are a lot harder to put together. If you are using an Excalibur you are already using En-Aero 2 and Paraylzing all the things so your 25% HP proc can go off. No reason your offhand shouldn't have a good additional affect as well.
This makes no sense, Relics's special stats on exist when their on main hand which is the only place Enspell II's work. Relics and Enspells are pretty much mutually exclusive to each other. As a general rule Eph sucks as a sword, it has a few specialized uses but in general Almace + Str Sword would be a better set. This pretty much forces you to use Zelus tiara to that you have more freedom in all your other slots.