We do a drill with players that are opening too fast.
Stand in a "stacked" position. This means legs spread like you just planted with arms out at shoulder height, glove or elbow pointing a target and ball pointing away from target with a nature arm bend from both front and back (equal/oppo). (allow both arms to bend at elbow as feels natural - some players are a little more straight and other are near 90 degree bend in the elbow with glove and ball out in front of body)
While facing 90 degrees from your target (assume right hand throwing - face third base while doing this in a throw to home plate) you will rotate your core (point you belly button at the target) and at the same time rotate your shoulder to bring the ball up and above your head without any more arm bend. On the front side "pull" your glove into your armpit/chest. Easily throw the ball. The idea is to teach your body to feel all the rotational parts in the throw.
As you get more comfortable with action, go from this position to hands together and start of stride. Then go into full wind up as that get more comfy and accurate.