Similarly the vast majority of that fighting force are, through sheer numerical density, going to mostly comprise 1. People the Imperial Navy has impressed into service and 2. People the Imperial Guard has conscripted into service. There'll definitely be volunteers sure, and crack fighting forces and Space Marines and God knows the boys in red aren't anything to fuck with. But we have the Sororitas, we can reasonably expect to get at least some number of Space Marines onboard absent the usual, uh, structural issues that come with chugging Chaos. And the rank and file of the enemy are going to be super vulnerable to, like, Ignatius standing on a gigantic golden warmech and giving a thunderous sermon on the sin of toiling in the service of cruel, uncaring gods.
Which we can somewhat reasonably expect to hit the people who Don't Want To Be Here like a fucking warship.
Solar bullshit and a comparatively small front to defend (a sector-or-three-at-
most) means that taking this place might legitimately shatter an Imperial Crusade in a pretty spectacular way. At least, as
@Imrix said, once we get our shit in gear.