A couple of points to note. 769s actually respond initially quicker, when the driver moves the traction power controller from off to a power notch when starting away from a stand quicker in diesel mode than in electric mode or than a 319 does. Engine revs rise with each notch taken however there is often no discernable rise in engine revs between power notches 3 and 4. As I understand it there is no field weakening in power notch 4 on a 319 when the traction power is supplied in 'DC mode', which is effectively what a 769 on diesel mode is.
One other thing that's odd is that the engine revs only really die down to idle when the unit actually comes to a stand. The driver will have shut off traction power long before this (and in any event braking in brake step 2 or more -normal braking on a 319/769- would disable any traction power still applied) but even when coasting with no traction power applied the engines still rev quite high until the train virtually comes to a stand.
150s etc don't have to be 'thrashed' before the brakes are released. Once the torque converter is actually filled (2-3 seconds) so long as sufficient traction power is applied to overcome any rising gradient, and even on the steepest gradients I drive of 1-in-40-odd, then the unit won't roll back even in just notch 3 power. Lesser rising gradients wouldn't need that much traction power.