You usually don’t “wave” your arms blindly in the air, you have a defined set of fingering positions and movements. Once you’ve learned them, they’re in muscle memory, just like typing on a touchscreen keyboard instead of a physical one.

You actually have a huge scale range. The octaves are defined by the location of your hand, the notes themselves are by the fingers. It’s supposed to be pretty accurate and makes sense from what I’ve heard?

I couldn’t think of always hitting the exact correct note out of hundreds just by a slider.

If you want something with a slider, theres the Stylophone Theremin