A couple of months back, I played someone with a very similar forehand. Very fast and kicked off the ground like a mule.
Stikes me as you need great timing to pull it off, but if you do...
If your racquet face is facing the ground at impact, something is wrong. It needs to facing the net, otherwise it will only ever go into the ground. Close to parallel with a low to high swing path will add topspin.
Not sure if I'm reading your description right, but if I am, it sounds like you are either pronating your wrist too early or else you are hitting too far in front of your body. If it is the latter, you will also have problems hitting any forehand other than cross court or straight.
The drill itself is just that...a drill. Just to get you to feel the racquet snapping through. Sounds like you have done it soo much that you've incorporated the whole move into your swing - and forgot it was only designed to help you 'feel'.
Far be it from me to say if the drill is a good or bad one. What I would say is that taken in isolation, it could lead to a very armsy swing. You still need to rotate your core and use your legs. He does - but he doesn't say it.