It's about acceleration.
Think about dropping a rock from a foot off the ground. Now drop it from the top of a 10 foot ladder. Now drop it from a three story building. Which time did it hit the ground with the most force? The higher drop gives the rock more time to accelerate, which in turn means it hits the ground with more force.
Similar (although not same) concept with a reach back. You are giving your body time to accelerate *into* the power pocket *and out* of the power pocket, which in theory will give you more speed and power at release than if you were only beginning your acceleration at the power pocket.
Now why doesn't that work for you? It works for the rock, so what gives? Well, a rock doesn't have to worry about rounding, or hitting the power pocket, or off axis torque, or any number of other things that can drain your power. Gravity is incredibly efficient when it's the only force acting on a solid object. By comparison, our bodies are not.
I think what you are doing is very good for your current stage of development. Keep it up! Keep throwing from the power pocket until that position feels natural. But you will eventually hit a distance wall, and to break through that wall you will want to start introducing a reach back.
As I've worked and learned about throwing discs, this exactly what I've concluded.
Early on all my timing was off so the X-step and reach back achieved very little. One of my playing buddies told me to go back to stand still which is what I did. Practiced that a lot, then began a half step and worked forward. Still a work in progress, but building up to a full throwing motion helped me a lot.
The other point I saw was about different body types. Patrick Mahomes can launch a football farther than most human beings with almost no windup and of course with a full throw it goes even farther. But, most of us are not superhuman that way and need to follow the same basic path to get a decent throw.