So the 2 videos you just posted are fantastic. I really like the tape on the disc to kind of explain the exact rotation of the disc as it should be coming out of your hands.
Even though I haven't tried throwing yet after watching these, I think one of my main issues is that I'm gripping too hard with my ring/pinkie fingers, which is preventing the disc from spinning out of my hand properly. I think that's what's leading to the disc leaving my hand awkwardly even when I get it out on a flat angle.
The very first video I ever watched and tried to mimic was the Beato video, and I actually had pretty good success distance wise just mimicking his standstill throw. The main thing is that I just couldn't figure out how to connect the throw from the pec with a pull back or any steps. I think I was twisting myself up too much.
This helps because I think this (and the third video you posted a couple days ago) puts all the pieces together in slow motion and helps you understand how to get there.