As badass as Cap is, everything special about him came from a bottle. Theoretically anyone who gets the SSS can be just as good as him. Wick on the otherhand is so badass that everyone in NYC knows him and most fear him. Even the police wont mess with John.
I think the fact that John is an ordinary human who has become one of the most feared assassins in the world makes him more badass. John is like Deathstroke, although he isn't genetically enhanced like Deathstroke, he also carries a strong reputation as an assassin.