Would motion aiming not solve that issue?
It's tricky to solve. Kid Icarus Uprising's style of gameplay is
very unusual.
Look at it like this. You have a targeting reticle, but it isn't locked to the center of the camera. In most shooters, moving the camera and moving the reticle are synonymous. Not here. You can very quickly and accurately aim the reticle anywhere in the current general direction of the camera.
Or, you can very quickly and accurately turn the camera to face any direction you want. Both of those things are very fast and accurate, but crucially, you can't do
both of them in the same motion. Aiming inherently requires the stylus to be touching the bottom screen. Turning the camera inherently requires the stylus to not be touching the bottom screen.
The result is a very hectic style of combat, where you can be powerful in any one general direction, and you can change that direction at will, but if you get flanked or something and you have to keep looking back and forth, it can get intense.
It's difficult to replicate this system without the touch screen. Not impossible, but hard.