The funny thing is, I remember, a few years ago, figuring out that that sort of whip and snap, was why I got such good spin on that serve. But, until recently, I couldn't get that same kind of snap on my pendulum even thought the pendulum was always decent. Now I am getting more of that whipping action in it.
But this video gives me some good ideas about how to hit my FH more like LL Beary.
IMHO, for you, it's largely the grip on that forehand. It's set up in a way that gives you good hook but it locks the wrist a bit more than some people think. IF you were a full bodied looping player, you could probably get away with it.
What you do with your wrist and what Brett does are not as different as you think, obviously. There are reasons why it looks different, and reasons why Brett's usage may be at a higher level than yours, but the overall idea is the same. On this serve, I am trying to come round the side of the ball and the paddle angle is a bit more horizontal than yours so that is what drives the different appearance.
The level of sidespin is massive. The last time I used to get this level of sidespin relative to my spin ability was when I was 1500 and improving my backhand serves. That's when I started learning that spin isn't everything and it was worth reducing the spin in order to be able to handle the ball sometimes, though the threat of the heavy spin was always something to keep around for certain points. When I used to get this level of sidespin on balls and my opponent pushed the return, I would push the next ball right off the table sideways or long.
For me, I discovered this whip thing while practicing high toss serves when I was doing through one of my 1800-1700 dip periods. Once I figured it out though, or something like it, I just stopped having bad losses to pips players.