Looks to me like you're releasing the disc waaaay early. Doesn't seem like that disc is ripping out of your grip at all. It also looks like your pull is too low and your upper body/front shoulder is opening up too soon. I think the front shoulder opening is what's making it look like the disc is coming out too early, I'll post a video that explains that better than I can. But the long throwers tend to keep that front shoulder closed as long as possible and rip the disc across their chests and let the disc get to their right peck with the shoulder still extended before they accelerate late and induce that hard snapping motion, which is where distance comes from really.
low pull, missing right peck
early release/ front shoulder open
Will Schusterick: Closed front shoulder/ pull across chest/ disc to right peck with elbow still closed
And finally, video explaining the closed front shoulder and snap ideas that I was talking about.
And I guess I'll add the slow mo of Will from the still image I posted