wallow in the corner ... would that be from the decrease rebound damping or the decrease spring preload?
The downside of softer springs (less preload) and less rebound is that the bike will squat more due to sag, and rise more on the brakes, due to less rebound. So, basically on the way into the corner the back of the bike will rise. Once the apex is reached and the gas is applied, the bike will squat again, causing a "wallowing" response.
Both of these effects is fairly minor with just a change to the preload and rebound damping of the stock shock, but the effect is there even with the preload and rebound high on the stock shock. Obviously, more prenounced as cornering speeds become more aggressive.
A better shock tends to have better control of the "high speed" compression (usually bumps) vs the "low speed" (spring control).
I'm using a 1200 shock on my 600, which is better than the stock 600 shock, but still not as good as better suspension components. (the old cost vs performance compromise)