The demo has the right instincts. In 112 words over 46.8 seconds, roughly 2.4 words a second, it gives you a ruined hive, a Space Marine before a shattered banner, a rogue psyker and an Imperium buckling under its own weight. "Victory tastes like iron and ashes" is the kind of line this fandom likes.
It also carries filler. "In this faceless chronicle" talks about the video instead of the war, and "hearing the marching Vox" means little, since a vox is a communication device. Swap those for a named world and a named chapter, and the same runtime carries far more lore.
On screen, the frames are dark and cinematic rather than flat and comic-like: a hulking armored figure with glowing vents, Guard-like soldiers charging through mud, a banner bearer against a burning sky. Those work. The last frame does not. It shows a neon-lit man with a red visor that looks borrowed from a cyberpunk film. Regenerate stray frames like that before you publish.
The ending asks viewers to comment their faction, the best call to action in the script. Every 40k fan has an answer, and most will defend it.