I think I’ve figured it out. The Pro model iPhones typically come with more advanced camera features.
In particular the True Tone flash feature was advertised as the most advanced mobile flash on the market. Now I needed to know why.
So I stopped down my SLR and you can actually see there’s an LED matrix behind the flash lens. It appears to replicate exactly what a speed light would do, but without moving the lit element.
That’s why the low light flash performance of these phones is so good. It does what a speed light does and changes the beam pattern based on selected focal lengths.
I’ll see if I can take any acceptable photos to demonstrate.
Edit: found this marketing graphic that demonstrates better.