Thing is the game is suppose to follow fluff more then tabletop. In fluff marines in regular power armor take hordes of guys firing lasguns and autoguns with "minimal" damage (burns and bruises that would have more effect on a regular human, but thanks to a space marines constitution heal nearly before they notice the wounds. This is something else that the space marines lack, healing is done only with the apothecary, which i find funny, as you are playing can heal from a 7.62 round to the ribs in a matter of moments, you lack regenerating health, while other games "normal" people can heal from 3 loads of deer slugs to the face like its nothing).
Another thing this isnt a tactical turnbased thing, Spacehulk DeathWing is a first person Shooter, so its possible to have several of these guys just unloading on you at full auto firing dozens of rounds cutting you up. I could see them over time doing something, But not as fast as they are right now. Terminator armor is suppose to be several inches of ceramite and adamantine, things that make modern day armor composites look like worn out tin. Granted their gun tech would be better as well, but autoguns are considered bottom barrel weapons with the lowly lasgun sneering down upon it.
If you wanted to compare properly, without hyperbola (like i did) i would say a Space marines standard power armor would be more equivalent to the IFV armor, while Terminator, which usually was suppose to require anti-materiel weaponry, Plasma, Meltas, Lascannons, heavy bolters, power weapons, ect. But here we are with a service rifle thats usually relegated to service in the PDF to help stop against pirates, raiders, and riots, cutting down armor used by the Elite strike force of the Imperium, that is commonly used in fights against other elite troops.
Im not saying they shouldnt be in the game, but they shouldnt be smoking terminators that easily. They should be support for the genestealers (they actually do almost as much damage as a genestealer) and the heavy weapons (so far you can run into guys with missile launchers, which yeah, anti-materiel) let them chip away at the armor, but your main threat should be the heavy weapons, genestealers, and other things your running into.
One additional thing, and this could go with the space marine constitution and durability, the moment your armor is penetrated (another issue, the amount of damage. A gene stealer spreads its damage over the length of a massive swipe, as opposed to the tiny hole a rifle would leave) your dead. Which is fine, against enemies who do massive damage hits, a genestealer should be tearing a marine apart, but against lasguns and autoguns..
They have The Secondary Heart, so if the first is damaged they can keep going, And in addition to that can help increase blood flow and pressure when needed.
The Ossmodula: Causes their bones to grow even more, which is why so many of them are depicted as being around 7 foot tall. Also allows their bones to be reinforced with ceramite and other supplements increasing density and strength. Also causes their ribcage to develop into a mass of armored interlocking plates rendering it almost completely bullet proof.
The Biscopea: increases muscle growth and density, which makes it so their muscles could also stop high caliber rounds.
The Larraman's Organ: releases a material that fills the blood of the recipient, when exposed to air it forms super hard and durable scabs to keep them from bleeding out and promotes fast healing. (novels have scouts healing from rifle shots in minutes leaving only a minor puckered scar)
The Multi-lung: a third lung, increases oxygenation of the blood, and can be used to breath under water (original lungs sealing at the time)
The Sus-an Membrane: an implant that when mortally wounded the marine is put into a state of suspended animation allowing them to survive until help comes (or the enemy finishes them off). When your "killed" your just dead, no chance for the apothecary to come and revive you as he should be able to, instead your stuck waiting for a respawn timer.
And by their powers combined! SPACE MARINES! ARE! CHEESE!!!!!
Well... You get my point.
I dont want them to be some unstoppable killing machines of which there is no chance against... Bt if im playing a space marine in terminator armor, it should feel like a space marine in terminator armor..