I wonder if at any point in the Logitech design process they tried to analyze the moment of inertia tensor to see if the sensor is aligned with the shape's principle axes. If not, the sensor can technically be misaligned to how the shape tends to move.
It is a truth universally acknowledged, that the comfort of a Logitech shape, is inversely proportional to the R&D put into its making.
After a calibration on the surface here I can make straight lines, no problem. With that said, I don't like to where they point the sensor, you really have to play a bit to get used to it. I prefer the G Pro.
If I hold the G403 in the most comfortable way the sensor will be slightly misaligned in my hand. If I hold it with the senor aligned I start to want to use another mouse. I sent the mouse back because the shape wasn't good for me -- I was always fighting to get comfortable while maintaining control.
The Pro was fine as it's a symmetrical shape. Main reason I continue to use symmetrical mice.