arms are fine, technique is good.
Most of these guys over think things
The left arm is actually helping with balance and follow through. So don't change any of that.
The little crouch before the throw to add extra power to the legs (you probably don't even realise you're doing it) is particularly good.
There's a lot more power comes from the legs in slinging than most people realise.
The thing to try if you want to increase accuracy is to stop the rotations.
Just do a straight sidearm throw without the balearic fiddling around.
It's ever so slightly less powerful but much much easier to be accurate with.
30 seconds in.
Try that. The compulsory balearic rotations were addded to make the target competitions harder.
A non-rotational sidearm style has more or less the same power and is much much easier to be accurate with.
You're using a fairly long sling so sidearm is never going to be the most accurate style.
Greek or fig 8 is much better suited to longer slings and target shooting.
And I am very jealous of that beach