What Erik said. Pressure has to go a bit more forward into that front foot on your downswing.
But to be more specific with your lack of a flat left wrist and no lag, your arms stay too loaded on your downswing, and you don't extend your trail arm soon enough to get the trail forearm more forward on the downswing.
Case in point:
Trail forearm is lagging. Left arm is lagging. The club head is being thrown.
Take Sergio Garcia for example (all pros do this though to varying degrees):
His left arm is less loaded against his chest. In fact, it's not loaded against his chest at all at this point. His right forearm has traveled down further. And he has less bend in the trail arm. As a result, he can sustain lag much later and also, the release will just naturally occur at the correct time. This is why your left shoulder has to raise and the right shoulder has to drop in order to reach the golf ball. You'll have a helluva time trying to hit it straight or solidly with consistency when the left shoulder raises and the arms stay loaded.
A lot of the time, we as golfers are told that the swing is "body driven," or that "the arms come along for the ride." That's borderline mediocre advice for someone who is all arms (like most high handicappers). But better players tend to forget that -- duh -- we gotta swing our goddamn arms and we can't be all body.
There's a rate at which the arms have to swing relative to one's body motion. If those two aren't in sync, you get into positions like you are getting into on your swing video.
Swing your left arm down across your chest better. Drive your right forearm more forward. Extend your right arm. You'll sustain lag much later in your downswing, presuming of course that you can also increase front foot pressure to shore up that weight shift you have. All this will stabilize that faulty shoulder rotation.
Cheers, mate. Hope that helps.
PS- Start a swing thread.
For further study on this, please refer to this video here, made by resident moderator and teaching professional Mvmac: