Fault or not thing is oda made it clear that shock wille was hit because BB was careless.
Anyway, even if it was hit, point still stands - difficulty of this fight will be determined on the basis of how much BB struggles in putting law down.
As of now he used one normal attack by riding on horse while law already used his second strongest attack which BB endured it. This isn't getting passed above low diff.
Now he is on ground and ready to use combo of Yami and gura - this will determine the real difficulty which based on spoilers of Chapter 1065-1068 is Law is getting negged/low diff (I have insider info)