Tricky muscle group to hit. With literally all available rear delt exercises you face a poor strength curve. Additionally high loads are hard on the shoulder joint and other muscle groups are likely to take over.
Especially the traps are your biggest enemy when training rear delts... or delts in general. If you pull back or up too much, the traps are the main mover and you shift tension off your deltoids to the large back muscle.
That's why we have to manipulate range of motion (ROM). I certainly agree that full ROM (of a muscle, not a joint) is best for hypertrophy, but with the delts an exception has to be made. The ROM where you can effectively place tension where you want it to be is very short.
That's why I don't pull apart the band all the way and perform these 'pulse-like' reps. If I'd pull the band any further apart I'd feel my traps working. So there's a difference between a regular band pull-apart and pull-aparts that are done to isolate the rear delt.
Shoulders also recover very quickly.
I'm sure you know this already. Just remember the last time you changed a light bulb and your shoulders started to ache. You bring your arms down for a few seconds and they feel fresh almost immediately. Shake it off and you're back to changing light bulbs.
How can you achieve this? Supersets, tri-sets, giant sets with very short rest periods (30-60 seconds) and ultra high reps. Since we cannot hit the target muscle with high loads to create a ton of muscular tension (see points above), we have to use a different path to more muscle: blood flow, cell swelling, metabolite accumulation - that's the way to go to safely hit the rear delts.
Here I perform a superset of band pull-aparts and prone laterals. These are performed in the bottom 1/3 of the ROM to reduce trap involvement. The first person I have seen do these was John Meadows. The focus is to not let the dumbbells touch and aggressively pull them to the side. The movement looks easy, but is in fact brutal. I'm not just swinging the weights here. With every rep I have to fight hard to keep the steel from touching.