There's nothing seriously wrong with your approach. Here are some observations and food for thought. I'll list each observation then tie them all together.
Starting with your arm straight down is okay but the way you do it is not. If you stop the rear angle video on your first step, you will see 2 things. One, you have no upper body angles. Two, the ball passes your right leg going inside out.
Step 2 should be directly in front of step 1. Since this doesn't take place, your finishing position at the foul line will be right of where it should be.
As your ball comes back forward, because it was started inside-out, it remains out and then come back down outside-in causing your shot to also be outside-in. The Brooklyn hit could be expected from just watching the first 2 steps.
All of your movements seemed a little bit mechanical. This can be caused by being in front of a camera
, or the reasons are more likely that having no upper body angles, you can't get into a athletic position for the final delivery.
Okay, here's how to tie it all back together to get you in a more relaxed athletic position at the point of release.
If you start with your left foot slightly ahead of your right foot, this will open up the front of your upper body before you ever take a step.
Not only should your upper body be angled slightly to the right, your upper body should also be bent forward slightly. The result of these 2 upper body angles are to allow the ball to fall straight back under your right shoulder on a slight outside-in line.
Here are 3 videos to show you how to practice the correct upper body angles. http://bowlingknowledge.info/index.php?option=com_content&task=view&id=229https://www.youtube.com/watch?v=2NhM3tights&index=3&list=PL067F4774D3519BC8http://bowlingknowledge.info/index.php?option=com_content&task=view&id=229
Your ball should not pass your body coming back until your second step is almost complete and in-line with your first step. This simple rule is what allows your ball to clear your body on an outside-in line coming back. Failure to clear the right leg forces the ball out to the right going back which will force the ball outside-in coming forward.
In real-estate, the 3 rules are location, location, location. In bowling, the 3 rules are relax, relax, relax.
Proper body angles and a relaxed starting position will allow the ball to fall directly backward in a nice relaxed swing slot. done properly, your head will be over your swing slot line. In your current approach, your head is nowhere near your swing line.
Stay relaxed as the ball goes backward and comes forward. Allow the ball to swing freely, don't throw it. The only time you need to do anything is to add a little extra impetus on the ball after your thumb has cleared.
Too often those who start with their arm straight down, lock that arm and do not allow it to relax. That means everything during that arm-swing will be restricted by tight muscles. Relax your hand and that will relax your wrist which will relax your forearm which will relax your elbow, upper-arm and shoulder.
Done properly, you will get more speed, more RPM's, throw more accurately with less effort.