Didn't read the whole thread but...
drop is not deep enough.
this is because you are arming it right after the trophy pose. you can see it in the slowmo. the racquet should drop because you are pushing off from the legs and uncoiling the torso. that will cause the racquet to drop on it's own. in you slow mo you can see after the trophy your arm goes to the left right after trophy. this is because you are 'winding up' to arm it. from the trophy if you are relaxed you should just push off w/ the legs, uncoil and it will drop right below the right shoulder and it will be lined up w/ the ball, unlike now where it semi-drops over to the left and you have to bring the racquet back over to the right.. you shouldnt feel/try any arm action until quite a bit later in the stroke.
maybe someone mentioned already but grip looks a little too eastern imo. more towards continental will give you better rhs and pronation.
and... you are hitting on the way down!
you have to be striking the ball on the way up. up the mountain as they say.
left arm goes down too soon. gotta keep it up longer.