One thing you've not mentioned is your weight when riding, and how your bike is typically loaded. Factory shocks, whether standard or ESA, are a compromise in setup. Factory shocks are best set for the "medium" rider. So for North America, I would guess that to be a rider abour 5'-8" tall and about 225 lbs in full riding gear. If you are a rider at the light end of the scale, the factory setup may seem harsh and you'd need to adjust to the lightest preload and softest damping rates. A rider at the heavy end of the scale would need the highest preload and harder damping rates. But not being in the 'mid-range" of the factory setup limits the range of how the suspension can be set for you. That's why one bike may ride great for one rider and for crap for another. But a quality suspension is set up for each specific rider, his weight, his bike loading, his riding style, at the middle range of the suspension. This gives the best initial ride with broader adjustment capability.
On short, sharp bumps (actually drop-offs) if the rebound damping is too high, the shocks are always trying to restrain the extension of the suspension slower than it could extend to "step" down the edge, and the bike feels like it just drops or falls over the bump. In some cases of multiple sharp bumps in a row, high rebound damping actually causes the suspension to keep compressing almost to the point of no active suspension until it has a chance to "stretch".
But then on the bigger bumps/dips, too high a compression damping causes the suspension to "stiffen up" too quick and not allow full travel to be absorbed by the spring. On bikes with no rebound damping it gives the feel of the bike pogoing over the bumps.
On the older Jap bikes many of us grew up on, the easy (cheap)answer was to "over-sprung" the bike and "under damp" the compression damping, with no rebound damping. But all better suspensions are usually lighter, longer springs and more refined damping. The lighter spring allows for easier initial wheel travel and the better damping slows the suspension action near the limits.