I am by no means an expert in this, but I don't see how the servo speed is more important on the throttle/brake servo. I see your point where you index the time from full throttle to full brake. Yeah there would be a difference, but only hardly noticable when going from full throttle to full brakes. How many times that happens on an average track with usually one long straight away. Only once two times max I would say. Turning from full left to full right can happen tens of times a lap. From that point of view speed on steering servo is more important to me. It's always better to have it and dial it down (if you can..) rather than not have it.
I usually loose more time braking too hard when the tires don't have enough traction and start locking up. I guess it's a question of an opinion and what everybody likes.
Good discussion though, I like it.