Race track use, flat sides are great. Around the street, normal driving, not as good as a well tuned CV carb.
CV carbs, when working properly, give better low RPM and throttle change performance. Flat sides can bog on large throttle changes. Racing is mostly large throttle conditions, not stop and go traffic....
Fuel economy suffers too with a flat side.
It like asking are racing slicks better then regular street tires?
The answer depends...If you are on the highway in a light rain, racing slicks are awful....
If you are racing, racing slicks are perfect for the job.....