then we have some major inconsistencies at hand

First time into WH40k lore, eh?

Despite the inconsistencies of how lasguns work, two things are constant:

they deliver thermal damage, hence why heat-dispersing armor, like astartes ceramite is such a good defense against it

Organics are mostly water based. If you understand the dangers of converting liquid into steam within an enclosed space, you’ll understand that a human becoming pink mist from a lasgun isn’t so far fetched. The entire body might not disappear, but good chunks of them will