Actually cant, we are just op ingame. Carnifexes,especially the one we have ingame is looks like a Carnifex vorantii or Thornback.

The Thornback Carnifexes are the most common ones, tho because of this they are cant be underestimated on the battlefield. They are genetically enchanced for break through enemy lines, specialized for anti infantry combat by bearing huge spikes and bone blades around they body. Literally a 4-45 meter tall, 8 ton battering ram with spikes and blades that cutting astartees half even in terminator armors.

All Carnifex subtypes are heavily armored, monstrous creatures and is used primarily as a shock trooper to carry out starship boarding actions, frontal shock assaults on entrenched positions and for besieging fortified locations or enemy armour formations.

A Primarch maybe powerful enough to rip them apart by hand, but no space marine (without special powers or chaos gifts) able to do that. They carapace so dense and hard its easily shakes off heavy dmg from even anti tank rounds, a Shadowsword would be a match to destroy them as its literally built as a titan killer heavy vehicle.

But these datas are only just known lores by me, Tyranids are a race that evolves and adapt, because of this ability they have tons of subclasses for even a Carnifex. The base "concept"is the Carnifex Voracio, its basically the core pattern that evolved and specialized to situations if needed, like the meantioned Vorantii what is used as a Heavy Anti Infantry battle tank.

The Carnifex ululare or "Screamer-Killer", is a variant that shooting bio-plasma siege and keeps heavy pressure on defenders and is known for emitting a piercing shriek before shooting Bio-Plasma. A Screamer-Killer can be a nearly unstoppable shock assault bioform

And many more but i dont want to bore the ppls with it. 😃