Difficult to say, it's been a long time since I read Heretic, and I never liked the Word Bearers to begin with.
This is a problem I have as well. I never liked the Word Bearers before The First Heretic
, and despite ADB's brilliant writing and story, I still just don't like them. And that reason alone will always, sadly keep that novel out of my top list when contending with the likes of Legion, Prospero Burns and Scars