No, I would rather get an allusion to the fact that Mortarion changed his ways AND get a short story that fleshes that out. Something like Mortarion pausing for a second after butchering his bodyguards and then squashing a momentary feeling of regret. Then, saying something like how only [however much time passes between Scars and Vengeful Spirit] ago he would not even have considered what he had just done, but that he had come a long way since Terathalion, where his eyes had been opened.
Or something to that effect.
Instead, I got a novel that went about as if there was nothing unusual about Mortarion pulling a 180 with his most fervently expressed moral stand. Then, almost seven months later, I got a story that purported to explain this.