the deception im talking about is sidetop vs sideunder because the pendulum or reverse pendulum motion are quite similar even on pure sidespin. Top & under deception is extremely difficult to disguise that was my comparison. What do you mean by "on" axis? You seem not to understand what I was explaining, Sidetop sideunder and pure side can all be created with the same motion before and after contact. It is also a matter of timing, contacting the ball at different phases of its descendance,maintaining the same "shoveling" action (from side, then down, then up after contact has been made)
I see what you're saying, and I was saying the same thing for pendulum underspin serve, with the same type of deception except rotated 90 degree.
What on-axis means: the ball can rotate in 3 axis. top/under is one, left/right side is another, on-axis is the third with axis towards the receiver.
In your example, the variation on the sidespin is moving the racket up bit more or down bit, but in the same plane as for sidespin so it's harder for receiver to judge. In my example, the variation on the underspin is moving the racket to one side bit more, but also in the same plane so similar hard to judge. The result if they push is pop-up in the direction of the axis spin you apply, because there's less under than they expect and axis causes some side-like reaction for pushes.
The whole point of deception is to create a fast motion where before and after contact the motion is the same. This "Shovel" technique is great because the nature of the motion creates the deception making a sidetop serve look like sideunder because the hand seems to "shove" under the ball and then going upwards after contact, giving the impression that the ball has underspin
This is another type of deception where the contact point isn't where it's pretend to be. In the video it's earlier but server keeps swinging to sell the backspin. I do the same idea but much simpler in a regular underspin serve, but the ball is toss slight more back and contact before normal point, so same motion but much less spin than normal. When you try to do complicated stuff like in the video, unless it's perfect smart opponent will know something is up.
On a re gular pendulum serve , at least in my eyes, is much harder to hide the spin because the receiver has better vision of the contact point without the playing hand getting in the way . In the shovel service, if you manage to do it fast like this guy does the follow through somehow "confuses" the receiver more compared to a pendulum serve where the playing hand can follow through without obstructing vision of the contact point.
Miu hirano is a great example of this service
I think the shovel for this is only more effective because few people serve that way, so most aren't use to figuring out what's wrong if it's not spin they expect. Some portion of penholders do shovel because it's more natural motion for them, just like their push shot.
There was some serve advice Werner Schlager gave about his serve where the racket come from below the ball, and mixes in both what you're talking about above with sidetop/sideunder and quick change in racket direction like you say about this shovel serve, to get top or under. It's something unique he did and I would use sometimes, but people I practice with who've seen it a bunch stop being deceived because I never had the motivation to perfect the motion. But they still fall for the simple "dumb" things like more/less spin or even surprise long underspin after couple normal ones. The point being unless you want to put countless hours like a pro, people who get fooled will get wise to it and it stops work much quicker than it takes you to master.