I was looking at the Power Fist and I noticed it still has the unwieldy trait while a weapon of the same design such as lightning claw doesn't .
It's not the size, a lightning claw is bigger as well as weigthing more then a powerfist so why is that ? I always assumed it was like this in DH and RT for design, lack of powerarmor or whatnot but for an Astartes in MK VII powerarmor ? that doesn't make sense.
Also we have at last one fluff entry, that I know off, in which a powerfist was used to block the Avatar's sword. Sure the Gauntlets of Ultramar are not exactly normal powerfists but the design is still the same.