Hasn't a Space Marine used a power fist to blow someone up? It's in the same novel that reveals that power fists have a stun setting.
There's a few examples of Marines at least using powerfists to simply kersplode people.
There is one short story where an apothecary plans to use his powerfist as a demolition charge in a suicide run to take out a Dready, and he cranks it up to max output. Whilst on the way, he smashes a Berserker with it, and is rewarded with a red smear and a light rain of armour fragments. He also uses it as a sort of shock weapon, placing his palm against the armour of other marines causes them to spasm and writhe as the powerfield is conducted throughout their armour. When the fist actually goes off as an adhoc explosive charge, its fairly impressive.
A chap in Deathwing demonstrates some more variety of use, pulsing the field of his gauntlet to fry the guy clutched in it, as opposed to simply using it to make the target more malleable, which appears to be the default setting for most powerfists. A heavy powered gauntlet, combined with a powerfield to let you dig through the material you are grasping at more easily, and the ability to put extra muscle behind a punch, which seems to result in a larger energy release from the powerfield.
So you can rip and tear, or simply use it as a bludgeoning weapon.
There are two known examples, one as a relic of the Golden Age of Technology in the original Chem-Dogs writeup, and the other the Sollex pattern energy blade produced in the Calixis sector by a mechanicus order devoted to understanding the laser, and based on technology reclaimed during the Angevin Crusade. They are rare and expensive.
It doesn't make much different, but the Sollex guys are plasma fanboys, its a plasma sword of doom. Eisenhorns is your basic sci-fi laser sword
The Eldar (who must possess the technology, as their knowledge of lasers exceeds the Imperium's by far) may not deem them fit for full scale battlefield deployment but that may be for a number of other reasons.
It might be rationalised that they use wraithbone blades because it allows them better control, the whole psychic substance might allow the limited telekinesis available to your average eldar to be developed into the bullet deflecting, sword throwing and so forth of Aspects and Exarchs. Warlocks and Farseers won't use them because they wouldn't have the psychic helix built into witchblades etc.
Plus, maybe Asurmen didn't like flashy laserswords, so he never let anyone play with them.....
I think a big problem with chainsword design is that illustrations are often informed by models, which suffer from heroic exaggeration, and we end up with a weapon with a cutting edge far smaller than the thickness of the back of the blade mount. Extremely fast moving tough and monomolecular cutting teeth aren't really enough to explain how the things cut through solid armour. I'd like to rationalise it by saying that many models might have the low level powerfield that Eviscerators have. Eviscerators being giant two handed models.
So it is highly possible that Space Marines use larger and beefier Chainswords than the ones used by the rest of the imperium.
Its pretty much a given that they do. Pretty much all their equipment is larger, usually armoured and so on. The standard chainsword of a Marine could actually be the size of an Eviscerator for a normal human, which is why I like to think they will also have some similar form of powerfield enhancement.
Swords of any sort are really more rank symbols than anything for the standard guard, you get to wave it around and "inspire" whether or not this actually works, or should make sense is pointless to moan about.