Get the RL if you don't have a Gjallarhorn. Trust me. Running the raid with a huge DPS weapon at level 29 beats running the raid without said weapon at 30.
I've run a few raids with full groups of 29s but none of them had a good RL, and they were all green with envy when I was blasting praetorians and minotaurs out of existence in one shot while they peppered them with LMGs. I even ran it on my hunter when it was level 27, and that rocket launcher was still making short work of everything in sight.
Besides, if you level up vanilla legendaries from the Vanguard QM and get just ONE raid piece from normal, you can get to level 29, which is enough to run the raid on Hard, so there's no need for the Light Beyond Nemesis. You might get lucky and join a group on Hard at the Aetheon checkpoint and get the raid helmet, too.