Your arm is moving near constant speed the whole time, without any real late acceleration. I'm sure you were expecting to hear that though, its everyone's problem. The third throw was better than the first in terms of late acceleration because your shoulder rotation looked better.
You're starting your pull too early, and doing it with your arm. Try to keep your arm loose once you reach back and start your pull with your hips.
In the first throw, your shoulders are just spinning in a constant motion rather than helping generate power.
Your footwork and weight distribution during the run up look good, but make sure you allow your hips/legs to follow through.
We're at our best when it's from our hips