I've been having this problem and its been bugging me for a while. My brakes currently sucks right now compared to before.

Earlier i had my entire handlebar stolen and i had to replace my shimano tiagras and switch them for some campy xenon qs. Before i was able to easily skid my rear wheel to a stop, but after switching to campys i can't. I'm not sure is it my cable routing or the levers itself thats affecting the braking ability.

I've cleaned the brake pads and rim, and a curious thing I've discovered is by pulling the exposed brake cable under the toptube, it brakes far better than my levers, leading me to think that the campys just don't have as much leverage as the shimanos. Is that the answer and is there any other ideas to fix this? Also i have installed some cross levers too, maybe this is affecting my braking performance too? Any help is appreciated.