I disagree. Modern ICBMs accelerate very very fast. It has been a desired feature for survivability and decreased time to target since the 1960s. I once read that they accelerate to their top speed and start to deploy their warheads within 2 minutes.
I don't think it matters much. Faster acceleration makes the objects reach the same separation altitude and down range in shorter time. If the acceleration is faster, the stages reaches higher speed at a relatively lower altitudes or shorter section of the ballistic arch, but after separation the spent booster sections will continue at higher speed in the same trajectories and land at the simliar spot as in case of slower acceleration because the arch does not change for the same range.
I said not much because I know it matters a bit, faster acceleration means higher speed in a shorter time span. Air resistance increase faster than increase of speed, so the free travel of 1st stage is reduced, its drop zone would be closer, but the effect on 2nd and 3rd stage is much less to zero because they separate near or out in a vacumm.
Overall, in this test, the 3rd stage landed at 14.4% of the total range, it is too close to launch point that I can imagine to fit a typical ballistic trajectory.