Superhuman and 40k are honestly pretty easy to reconcile. Physics get bent and broken pretty similarly. The only big differences are in the extremes of individuals and scale of setting. Henri is the only person in Superhuman that MIGHT be able to truly harm or change a Chaos god faster than MC could, but he'd still have to do it the slow way outside the Warp, and it would take a really fucking long time because that universe is vastly more populated. Sending him into the Warp is begging for a super-apocalypse. Malik wouldn't do well in there either, he'd lose his shit pretty quick. Bernhardt could delete pretty much anything short of a Chaos god in there, but it all respawns anyway. You can't beat them by killing things unless pretty much everything capable of thought goes extinct.
The serum level 5s could mostly do fine being in the Warp and fighting most things. The highest tiers of demons wouldn't be that different from normal A and S rank monsters. They could bully Nurgle in teams and some could probably do it solo. Anyone lower than level 5 except MC and particularly strong Power/Body/Memory monsters would have to worry about Corruption for sure though. I wouldn't even include Power monsters but WW made it explicitly clear with Indra that it correlates to resisting mental powers/changes which is the only reason Syla lost.
The serum level 5s could mostly do fine being in the Warp and fighting most things. The highest tiers of demons wouldn't be that different from normal A and S rank monsters. They could bully Nurgle in teams and some could probably do it solo. Anyone lower than level 5 except MC and particularly strong Power/Body/Memory monsters would have to worry about Corruption for sure though. I wouldn't even include Power monsters but WW made it explicitly clear with Indra that it correlates to resisting mental powers/changes which is the only reason Syla lost.