Well, BFTBG is simply not meant to be a deep, complex storyline with many plot twists & extremely interesting believable characters, eg. Gaunts Ghosts & Daemon World etc. If you picked up the book thinking it's gonna be something deep and complex like Dan Abnett's works, then you're mistaken
Its a book about an ASS-KICKING champion of the ASS-KICKER GOD. Plain & simple.
Like the script of a Chuck Norris/Steven Segal movie being made into a book. What else can you expect from the Blood God ? Khorne leaves the complex plots & scheming to Tzeentch, who's minions got their ass kicked in the book anyways
Its nice to have a pure action book like this come out once in a while, after all the drama and plot twists of the other BL books. The only other book like this from BL that I've ever read was Mark Of Chaos, by Anthony Reynolds.
Edit : Well he does transform into a Daemon at the very end of the book. In the Epilogue. As a reward for freeing the the Greater Daemon, he is granted Daemonhood in the form of wat look like a Bloodletter.
OK Back on Topic :
Could the Skulltaker not have just teleported to Abhorash's location & challenged him to a duel ? He's always looking to fight the best warriors, so why not go and challenge the best there currently is ? He's a Daemon, not a mortal man, so travel is not an issue for him.