"That's why I said "the left hand will get involved naturally just as the racquet comes through". What I'm trying to get over is for people not not force the use of the left hand and not involve it too early. It is hard in words."
Got it. I think generally ... it's easy to pick out on video when a players left arm/hand fires in a 2hbh. It's when the racquet head starts to rotate around the handle. For a player without the "butt cap forward lag", the left arm will fire immediately on the forward swing.
@Traffic 's recent video shows this type of 2hbh. Then we could look at mine, where I have "some" butt cap forward ... but not past the line like Djokovice and not as delayed on the rotation/whip. My left arm fires somewhere between past the back leg and the belly button. Then you can watch Djokovic ... and his left arm is firing somewhere around front leg.
Based on my 2hbh painful learning curve, I would differ on your description that the left arm "gets involved naturally". I spent a couple of painful early weeks trying to hit the Agassi straight/straight 2hbh with minimum left arm. I had hit a 1hbh for 4 decades, and based on Yandell's article, it seemed logical the easiest migration from and existing 1hbh would be straight/straight. About the 2nd week ... maybe by accident, I started thinking in terms of actively hitting with the left arm/hand. BINGO ... never looked back. If I was teaching a beginner ... one of the first things I would say is 1) everything relaxed 2) good backswing prep 3) get after it with the left arm/hand. I hear you, and think you are promoting the butt cap forward lag 2hbh where the left arm doesn't fire until time to whip/rotate. I agree... I just didn't find my left arm cooperated in the hitting part "naturally".