Then why are you
- ignoring it
- reluctant to change anything
I talked about star wiring and you said
Star wiring has nothing to do with ground loops. It has to do with noticing where the heavy currents flow and isolating those heavy currents from the light signal currents to avoid ground bounce. For example in that schematic you have the power ground first going to the mega and then on to the motor driver. That is exactly the situation you need to avoid.