I understand your frustration. If it were easy, everyone could and would be doing it. I'm pleased that you love the vault, it will carry you through this rough spot (I hope), you'll soon see a breakthrough, then hit another rough spot. Perseverance and determination are your friends! If you can find a PV club nearby, join it and get all the jumping and coaching you can.
As for your videos, I see several things leading to your "butt in the bucket". Understand that the last 3-4 steps have a HUGE influence on the rest of the vault.
1. In general, you need to JUMP UP at take-off. To do so, you need to be in a position, with the correct posture, to jump up with the pole overhead as high as possible.
1.1. You are not extending your top arm early/quickly enough. It should be fully extended before your take-off foot touches down. In addition, your bottom arm should be nearly fully extended as well at takeoff. You have a strong tendency to want to "hug" the pole at take off. This puts you on your back too soon and hurts your swing (which is needed to get your hips up - or get your hips out of the bucket).
1.2. In all of these vids, you are taking off "under" or "in", sometimes nearly by a foot. It puts you in a poor position to be able to jump up, and by the time your toe leaves the ground, you are already collapsing into the pole. This too hurts your swing. You need to have your step checked every vault until you consistently hit it.
1.3. The objective of the jump at take off, is to push the pole up towards the crossbar with both hands. In your jumps, the pole is stopping at the plant, and you are collapsing into it before your toe has left the ground. You need to be jumping up towards the crossbar, not into the pit (which is what it looks like you are doing).
2. You need to be constantly pushing the pole up - towards the bar throughout the takeoff and swing. I see you pulling in an effort to get yourself up the pole. This actually hurts you - it slows/stops pole rotation, and it hurts your swing.
3. Given your speed (which I think is pretty good), that the pole is moving to vertical, and you are landing deeply in the pit, you could be holding higher.
4. If you improve your takeoff position, your posture at takeoff, Jump at takeoff, and push the pole, you should see a big improvement in your swing. When that happens, you can focus on keeping your trail leg long throughout the swing and swing your feet to your hands.
4.1 High bar swing work is beneficial
Good source of videos:
https://www.youtube.com/user/ArtoftheVaultA good breakdown of the vault phases:
https://www.youtube.com/watch?v=LhqEdocpfcM