"Don't know that I'd agree with that. There are many factors to braking performance. Never noticed a dif between my dropbar and flatbar bikes that didn't have to do with the brakes themselves. .........
Drop bar braking postion does allow the user to squeeze harder.
My point is that drops allow a stronger pull. The wrist are stronger anatomally in the neutral postion rather than in the flat postions where several muscles are maintaing the postion and can not contribute to squeezing tha brakes
Don't have evidence to prove this translates in to pratice, other than if you get a grip tester the best results are achived in a vertical postion.
I could get anorak about which muscle groups are in better mechinical postion, but I fancy another coffee!