With Ben severing his connection to the force as to not be murdered by Inquisitors, he is a mere shadow of himself to begin. He’s hiding, like Luke in the movies. His stance a decade after Order 66 seems to be that the Jedi were wrong, and needed to fade away.
Darth Vader has always been a slower moving android, and toyed with his prey. Terror is in Ben’s heart now and Vader loves it. Vader even says it’s going to be a slow painful death he delivers, but we know this is untrue because of Episode IV Star Wars the film. It’s always been about protecting kids or enslaving them to become religious extremists; for either side.
Enjoy the ride! Critique it after you’ve ingested it in its entirety. Not 2/3 through. MTFBWY