It boils down to setup. Fade in the rear brake, yep never had fade in the front

. I am probably a 60% rear / 40% front brake user. I have no interest in joining the camp that says 90% of braking is done by the front brake. Only way I am putting that much brake input on the front is in a straight line on a smooth downhill.
Modulation vs. control, there may be some difference in perception. I agree that it is harder to lock up a smaller rotor, so if your definition of modulation is dependent on you having to squeeze the bejesus out of your lever to lock the wheel then a 6in would by that defn. have better modulation. Basically you only can lock the rotor by really clamping down on it. Okay, I can see that perspective.
Having not seen the south side of 200lb since I was in puberty I have a bit of a different view on the small rotors and modulation. On XC they work fine, but on an extended DH trail 2+minutes of heavy braking in steep terrain not so well. I cook the pads and rotors. Once they glaze or get too hot the modulation is gone. It is either off or on. So minimal power until I really clamp down and then finally some power, but no modulation between. Some people like this sensation, esp on a 6/8in rotor combo, as they never lockup the rear wheel so they go faster and leave the O'sh!t moments up to the front to save.