For what it's worth I have a few comments to add. There are some smart guys on here and I'm not sure I'm one of them! Jody seems to have the most insight on how the ZO system is truly designed so he can probably answer the question I will ultimately ask.
dn - I think you're spot on with points 1 & 2 and I can't explain #3. I can make sense of ABC123 to myself in my head but I try not to confuse anyone else with my explanations. I may be about to as I'm thinking out loud here... Maybe A, B, and C control setpoint overshoot differently as well? As you indicated, to get out the gates at an average of 34.2 and the skier pulls the boat down to X mph less than that for Y seconds you have to make up for that with excess speed for corresponding time. The integral of speed error over the course has to equal close to zero to get 16.95. So maybe A overshoots a lot for a short amount of time and C overshoots a little for a long time? I'm picturing a sine wave in my head where set speed is the X and speed error is the Y. The area above has to equal the area below at the exit gates. Then there is the question of ramp rates and delays but I don't want to go there. That is a large part of ABC123 and I don't have enough info to say.
All the talk is about throttle response, which is governed by the physics of the throttle blade moving, allowing more air into the intake, and then the engine injesting that additional air. This is relatively slow. The blade moves instantly with ETC, but the size of the throttle body, the manifold volume, pressure difference across the throttle body, and lots of other physical attributes all play a role. What about spark and fuel? Does ZO add power to the system just by opening the throttle or does it move those too? If you're not at the knock limit, you can add power really quickly by adding spark (the fastest ECM loop rates I've seen are in the order of 5 msec).
So Jody, is ZO a fully integrated power controller that manipulates spark and fuel in addition to air or does it just move the blade to let in more air like PP did? If that's the case, a video of the tach through the course might not be the whole story - and is probably filtered heavily anyway.