Wolverine has lost to Castle in fights plenty of times. He's just a guy with a healing factor, a bullet is still going to take him down, at least for a little while.
Having a knockoff kill Punisher doesn't respect the character; who is pretty important in comics from a philosophical standpoint. (A killer of criminals is an important concept to flesh out in a world where hundreds of individuals fight crime on their own terms. ) It's bordering on a poor concept for the story and bad writing. Although after reading the last post with Frank killing his resurrected family, I can understand that the writer just can't write. His poor choices yanked me out of the story and left me saying that this isn't the Punisher, this is out of continuity or fanfiction.
Regardless, its a nail in the coffin that is my buying marvel. Their stories are in a word: bad.