WhoKicking is as complicated as feinting is. There are weak kicks/feints and there are strong kicks/feints. There are people who cannot block/dodge and there are people that can. I think the whole kicking topic is as fair as feinting is. Training and Talent decide if you can dodge kicks.
I would say that 10% of the damage dealt comes from successfull offensive kicks in high level duels.
For example in the Ft69 against OneOrThree I did today, there were like 20-30 successfull kicks and we are both passionate kickers.
I don't know If I remember wrong but in Warband you could block everything besides stabs during kicking. I think only in the super high skill duels kicks very punished seriously due to movement?
It's similar in BL. If you miss an offensive kick the following happens:
-you loose the initiative
-enemy gets around you since you cannot turn -> harder to block
-you can be easier kicked since you stand still (yes this is used)