I worked with OEM alternator design and wiring for many years.
What they are doing makes sense. The power is coming directly off the junction point, instead of having to run to the dash wiring, the headlight switch, and then back to the lights.
But whether it is required comes back to my initial request: what's the voltage at the headlights?
Btw, the alternator voltage varies as a function of temperature. The battery wants higher voltage (max 14.7) at low temps, lower voltage (min 13.5) at higher temps.