Ok, I was curious [and bored] so I did a comparison of three power weapons. A Power Fist, a Power Axe, and a Power Sword. I set this up so that every weapon would make rolls with the most ideal attack that it is possible to make with the current rules. The Power Fist is only capable of making an All Out Attack or a Standard Attack. The Power Axe can make up to Swift Attacks. The Power Sword can make Lightning Attacks. I think physically made rolls for each, ten attacks [I'm aware that this isn't very many.] I only considered successes, since those are the only rolls that deal damage.
What I found out is that Unwieldy weapons basically suck, Unbalanced weapons are ok, and any weapon that isn't Unbalanced or Unwieldy is going to stomp any weapon that is. By extension, Lightning Claws are broken overpowered, they have higher base damage and pen than a power sword, higher minimum damage, and they scale with Degrees of Success twice. Most weapons Unbalanced or better only scale once.
You can read the data for yourself, the link is at the top. The average damage for a Power Fist is incredibly poor at just over 20. A Power Axe making a Swift Attack is literally twice as good, on average. A Power Sword deals about 25% more damage than a Power Axe when it uses a Lightning Attack.
Please note that I am well aware that 10 rolls each is an extremely small pool to be gathering data from. I would appreciate it if anyone could tell me how to make some more rolls, in high quantity, easily and with good readability. Ideally I would like a tool that lets me assign a weapon, then an attack action, WS and Str stats, and lets me makes a whole bunch of rolls all at once. Preferably taking the different attack actions into account and calculating those as well. I would make one for myself, but I'm not a programmer.
Thoughts? Comments? Suggestions to restore balance?
PS: This isn't a problem with rules from Deathwatch and older. There is no limitation on Swift or Lightning Attack, which means there is a meaningful trade off between parry potential and damage potential.