One of an 800-volt system’s greatest benefits is that it requires half the amperage of a 400-volt system to return the same charging speed, as multiplying voltage by amperage provides the charging speed. Higher charging rates incur more losses, so by lowering the current and raising the voltage, the whole process becomes more energy efficient.
Another win for the 800-volt system is that, due to the lower amperage current within the EV, thinner cables can be used.
I wouldn’t say it doesn’t matter. If your motors are rated for the full voltage (and why wouldn’t they be?), they will have higher maximum torque. Or you can use smaller, lighter motors.
I haven’t worked with EVs, so l but I did quite a bit with stationary, industrial, synchronous motors driven by VFDs. In that application, the V/f curve is used mostly to control torque and power efficiency. But the voltage drop isn’t that dramatic.
I imagine the EV brain would do clever things such as increase voltage to accelerate the car, while reducing it in cruise to reduce power draw. But there are clear advantages to having a higher voltage battery.