If you can watch the affects of a DP carb with a wideband sensor, you will notice that at a steady cruise and then go to WOT, you can see the richening affect of the twin pumps. The A/F meter will go rich immediately at WOT. This can be leaned out with the secondary cam and secondary arm adjustment (I have found that the squirter does not change the A/F much at WOT). But if you are rich at cruise to WOT then you are going to be allot richer from idle to WOT in an auto car. I believe that the trick is to adjust the secondaries on a DP to only give the engine wants and no more. Smaller engines like mine do not need the full 30cc's that a standard secondary pump provides, so limiting that volume is the key for mine. As others have said, it is in the tuning.
Since I have my WOT A/F ratio tuned to 12.8, I am now tuning the A/F ratio from a cruise to WOT and I almost have it. I am currently showing the cruise to WOT spike in the 12.5 range and I hope to lean it out to about 12.8. I have been as rich as 10.8 and changing the secondary cam and secondary cam to arm gap has allowed me to lean it out. The response after leaning out this rich spike is definately crisper now, even at lower rpms.
Next I will test my idle (foot on the brake) to WOT and see how that is affected.
I do know for a fact that too much fuel at any speed/rpm to WOT will kill the performance/response with a DP.

I am a believer that a DP is very tunable for a street driven car.