Do high-speed ailerons help with the roll rate control in non-FBW?
No it does not reduce the aeroforces: the hydraulic actuators that deflect the inboard aileron have as much of a force to apply as the ones at the outboard aileron. Force for deflecting a flight control surface is a function of dynamic pressure, surface area and of surface deflection.

As you state in the question, the inboard aileron reduces wing twist which could produce aileron reversal at high dynamic pressures, particularly problematic with relatively thin wings and high wing sweep angle.

The reduced moment arm affects the aircraft response upon aileron deflection. The problem with the ailerons is that a deflection equates to an end roll rate, as opposed to the elevator and rudder where a deflection results in an end angle. Many aircraft have a slow roll oscillation in cruise that the autopilot compensates for. If it must do that with an outboard aileron at M=0.85, the strong response of the outboard aileron makes it hard to not overcompensate. I have seen the inboard ailerons on a B747 do a slow deflection dance in cruise, while the aircraft roll angle stays perfectly still. 

Slow roll oscillation in cruise was a problem with the F100 for a short while, the gains in the autopilot could not be set low enough to obtain a constant zero attitude. Not really a problem, only in the perception of passengers looking out of the window. It was ultimately solved using different logic but unfortunately I don't know how they did it.