I'll definitely do some more testing, sure.
As I said, I feel like I have to do a bit too much once the player is in the air and I'm trying to perform a trick. Having to hold a button to not drop the ball, as well as press and release a couple of buttons and moving the right stick to switch hands and make moves, feels like a lot to remember and do all at once. I think something more along the lines of NBA Live's dunk contest from 2005-09 is better, where there are different gather options (one foot, two feet, one foot spin, two footed spin), and then different trick buttons while in the air that have to be held and released at the appropriate time to successfully complete the dunk.
While it may sound too simple, there's still the need to gather from the right distance, hold the right button long enough, and choose a trick that will garner a high enough score. There's also modifiers and right stick movement to perform 360s and so forth, so there are more complicated tricks that can be performed.
I think the biggest thing for me though is having to continue to hold down a button so that the player doesn't drop the ball. I feel that holding onto the ball should be an automatic action in basketball games, the same as dribbling. Not having to worry about that would help make the trick combinations a lot easier to master, and less contrived. With holding down three shoulder buttons, on top of moving the sticks, you kind of have to play the controller like a piano, especially as far as releasing them at the right times. I'd prefer to only have to hold down two shoulder buttons maximum at any given time, as that's pretty much how it goes with most basketball games.
I'd also suggest that it be very easy to pull off a couple of basic dunks, to give the user an idea of how it works. These dunks obviously wouldn't get high scores, and more complex moves will need to be mastered to win the contest, but it helps ease the user into the concept, and give them some initial success. It's like the Goomba in the original Super Mario Bros: it was added so the first enemy players encounter can be defeated in one hit, with a simple jump right on top of it. Those first parts of the game should be very easy, to draw players in and show them the basics, before presenting them with situations where they must learn and master more complicated and precise moves.