First of all you are left handed. Smart decision. 
I like the arm action and I recommend you do not do anything to address it directly. It is good to very good as it is. It is long and loose. Keep it. Hand break timing is about right. I do not think you need to change it. If on you next filming session, you can get the camera directly behind you, it would help to see your direction a little better. I would also like to see you work off the mound. I wouldn't make timing assessments based off of the flat ground. You may be a little late with your arm but I do not think that is the control issue, unless you are trying to mentally adjust it as you pitch. That will not work. Just let it happen.
Do you have arm pain? I mean ever. If so, where? That would change my outlook some.
On your wind up you take a step armside and (i think) continue a slight drift in that direction as you go to the plate. This has you throwing slightly around your body and makes the exact release point more critical.
Start in the stretch for now. Use a very slight inward flex on the posting leg during setup to bury your weight in the inside arch of your posting foot. On your lift, take your knee towards you nose or your left eye (just do it the same each time). Feel some coil or tension build inside the posting hip socket? As your knee is approaching the highest point feel the outer (back) of your posting hip drive your front hip towards the mitt. It doesn't need to be max effort just a firmly directed drive toward the plate. You don't bend your knee for this drive. It comes from the tension created in your hip from the lift. You might imagine you are pushing the rubber straight towards second from the inside of your posting leg. Have the side of your landing foot glide sideways to the mitt as as long as possible. It will turn to the mitt before you land. This should get you better directed. When you move to the windup seek to get the same feeling of slight coil inside the back hip. It doesn't have to be much. We are merely trying to set your direction straight to the mitt and not allow you to drift armside. I do not feel you collapse the posting knee more or earlier than many high level pitchers.
Have you had a growth spurt lately. It can take a while for your body and brain to sync up as you are growing. What year are you?
At the end of your video you look a little disgusted. You shouldn't. You have a pretty good base to build on and you will progress a lot faster if you will allow yourself to believe this is a problem you are going to solve and can keep the "I suck!" thoughts out of your head.
Good luck and stay strong,
Ted