There is one near court of oryx. Acolytes spawn nearly every 2 seconds

Loot caves are, like, sooooo Year 1! There's a half decent one on Venus. Turn right on patrol and keep going right to the end of the shoreline. There's a small building with dregs/vandals and a servitor. Clear them out then jump on the outside door frame (to the right). Then jump up and out (so you miss the overhang) until you reach the height limit. You should see them respawn on your radar. Run in, kill, repeat. Not the fastest method but easy to do and gets results. Once you get the rhythm you're looking at a 5/10 second rotation. Hope that was all clear enough. If not, sure they'll be a vid on YouTube. Edit: Or go to the Academy where Vex and Fallen are fighting by the downed ship. By the time you've killed everything they start spawning back in. Plus there's a chance for "enemy moving against each other" event. Plenty of fodder for engrams.