Motors can be difficult to reason about, as there are so many variables. So let's analyse a motor and keep the speed, torque and power output constant.
Let's say it has two seperate identical windings. Each winding, for the sake of argument, carries 1A and 10v. Now if we connect these in series, the electrical supply to the motor will be 20v 1A. If we connect them in parallel, the supply will be 10v 2A.
Both windings are receiving exactly the same power, and the motor is providing exactly the same speed and torque, yet the voltage and current at the terminals are different. In both cases the electrical power to the motor is the same.
We could regard the two parallel windings as a single winding with twice the area. In fact, some motors are wound with multiple parallel strands, as it's easier to do than using a single thick wire.
We can see that the speed constant and the torque constant change in exactly the same way, as we fill the winding space available in the motor with either many turns of fine wire or a few turns of thick wire.
Notice that the heat lost in our two windings is exactly the same, whether we connect them in series or parallel. So the efficiency of the motor is also the same whether wound with many thin or few thick turns. All that matters is the size of the motor to receive the wire, and the power you want to run it at.
Most people will match the speed, power and weight of the motor to their vehicle, and then choose a KV to get a terminal voltage at that speed to match a suitable controller and battery, not the other way round.