Soreness: First, soreness does not equal growth stimulus. I just have to put that out there. Go run a marathon or do 500 push-ups tomorrow. You will be sore as fuck for the next week but will have done nothing to grow big legs or a big chest. Also, you will likely never feel soreness in your glutes from any compound movement, ever, so don’t waste your time chasing that, ever.
Next, I am uniquely qualified to help you. RDLs happen to be my favorite exercise and I have a 20-year love affair with them. I just hit 585x5 the other day.
I believe the reason you are not feeling the exercise in your hamstrings and is that you are going too low and both your t-spine and L-spine are going into flexion in the bottom position. You are distributing the load across 4 levers, instead of two. Try this and let us know if it helps…
Move your feet closer together, no wider than directly under your hips. Point your toes straight forward, not out at a 45, like in the vid. At the top, squeeze your shoulder blades together like you are trying to hold a pool noodle between them and lock them in that position. Take in a big breath to create a big, high chest. Strive to your upper body locked in this position for the entirety of the set. Initiate the descent by thinking about recreating that photo shoot Kim Kardashian did where they set a glass of wine on her ass and using your hip flexors to pull your hips back. Continue lowering the bar by continuing to pull your hips back, rather than lowering the bar. The bar will lower on its own as your hips hinge. Continue to descend until your hamstrings feel tight. Then reverse the movement.
If you keep shoulders back, big chest, and pull your hips back with your hip flexors, you should not be able to descend much below knee height. At 2-3 inches below your knees, you should feel a full stretch of the hammies.
Get this form down and add weight, and you will feel it in your legs.