Arcade control is usually set to controller 3 position + controller 1 position for the left motors and controller 3 position - controller 1 position for the right motors. The reason your robot only spins is because you set every motor to have the same code, so doing anything will result in all the motors doing the same thing, but the left and right side motors should have different code.
It looks like you were trying to curve the values from the joysticks to make controlling the drivetrain easier, but the above code won’t work for various reasons. This thread explains how you can do it: Making joysticks less sensitive using exponential functions.