This just hit me like a cold night on Fenris when I was working on a possible list for next month when I was looking at Wolf Guard.
In 5th, the favorite package was to give them a combi-melta and power fists. My friend and I used to put power weapons in the Grey Hunter squads to balance that out as this option worked better than Wulfin.
With 6th, we have a new issue being they are “characters” when they attach to a unit. So, a power fist could be challenged now and killed removing the threat from the combat. On the other hand if you swap the power weapon for the fist, the Wolf Guard has a slightly better chance to survive but you take the loss of a +1 attack. Still, this is better than NEVER being able to attack at all if you get challenged (and killed) or you refuse and are unable to fight.
Many other Marine armies are going to take this worse as their Sergeant is usually the only model to have the option to take a power fist. This now comes down to a simple, challenge and kill concept that could push the popularity of the power fist back as time goes on if the Challenge system starts to be used in an aggressive format in games.
Well, this means I will be pulling out my figures tonight and doing a few weapon swaps!