Interesting write-up. I can see writing value is both these, and other approaches. I will share some outside thoughts.
I'm indifferent either way here. It's not the individual characters that make the setting tick, but the overarching themes and concepts coming together to paint a greater picture. All these fleshed out characters and colourful events are nice spice, and I am well aware that they are a major popular crowd-puller compared to the larger themes I focus on. People want heroes and villains and grand tales of daring-do. Man is not only a toolmaker, but a creature of stories.
Artwork by unknown.
One thing that a lifetime of creativity has taught me, is that I am always naturally inclined to go less bonkers and dare with less exaggeration than fine stories and settings such as Warhammer 40'000 call for. As someone whose natural inclinations are to write characters and events down to earth and without daring inventions, one cardinal lesson that I have learnt over the years is to always ask "how can we make this anymore bonkers?" while grinning during writing.
As such I can well empathize with Black Library authors writing up characters with magic powers and strange abilities in an uppity-hand power fantasy display. I would either have gone with Ollanius Pius being a fictive propaganda invention, or just an ordinary mortal who happpened to be present for a memorable self-sacrifice. From my perspective, Games Workshop dared to go further and do something crazy with it, for better or worse.
I don't care much either way. Why not indulge in some crowd-pleasing power fantasy plot and attempt to build up the drama? As long as the setting above and beyond its individual characters grow in an interesting way that is true to its own spirit, I'm fine with most details like these.
In other words, it is precisely the propaganda figure of S:t Ollanius Pius I am interested in. The story told to bolster the morale of Imperial Guardsmen across a million worlds and uncountable voidholms. Whatever core of truth or false inventions that exist within this story, works fine either way for me. Yeah, why not have a real hero's death wrapped within the layers of fiction? But he could as well have been invented from whole cloth during later millennia.
Artwork by John Blanche.