The main problem is that Marquess does not have the ability to ground any of his shock value stuff, to make people care. He has described the spoiler you mention as "cool." It's grotesque, and if it was presented that way onscreen then people might be fascinated. If it is presented as just shock value then who cares? It's the same stuff as the fire. They just shrugged off most of what was supposed to be a tragedy. Steph choosing to inhale smoke and burn to death instead of dying of cancer should have been very dramatic, but instead the only story to come out of it was dead-eyed lumps forming a boy band. Malachy's death was IMMEDIATELY forgotten so that Mercedes could try to make the Costellos less boring. And then there's Warren's return -- Warren basically pushed a man into a fire in order to get out free, and yet the whole thing is done so apathetically, apparently we're not supposed to care.
Supposedly the original fire plans had Brendan killing Amy. Sadly if that had happened it probably would have just been interpreted by many as another example of how complex the mumbling comatose Brendan is, and Ste would have just made a few whimpery faces before Brendan punched him out and then used him for sex.