It doesn't hold water because you can buy "knucks" which allow anyone to do STR+1 Physical damage with a punch.
If the cyber arm still has the give in the hand like a normal hand, then Knucks would work like brass-knuckles or a
roll of nickels: It stops the give, forcing the kinetic energy of the punch to all transfer to the target, instead of some
of it transferring to your hand.
Sorry, I don't buy it. In no way would any decent cyberlimb have the same "give" as a normal flesh and blood hand.
This sort of sounds like you are stretching to prove a point, or explain why the designers would have a metal and plastic cyberlimb do less damage than a pair of reinforced gloves.
Unfortunately there is no explaining it from a "lore" perspective. But from a purely game mechanics perspective? "Balance"? Sure (even though I don't agree). A dev from multiple editions ago hated cyberlimbs? Ok.
But there isn't a logical reason why someone with brass knuckles would hit harder than someone with a super customized mechanical limb.
Alternately, you could take cyber melee implants. All current melee cyber works off Unarmed Combat.
Still kinda missing the point. I don't want to claw at someone with razors or gut them with spurs. Just a good 'ol fashion cybernetic punch to the face! It just sucks that everyone else can do it better.
That's not exactly how I would have pictured cyberlimbs.
Anyway, sorry to carry on about this. This is clearly one of those Shadowrun quirks that will never change. Dragons, magic and laser guns are ok in Shadowrun... but for some reason capable full-body cyborgs are frowned on.
Every edition I hope for an improvement, but end up disappointed.
In SR4 there were the first full body cyborgs that used special brain cases and rigger vehicle rules. It was interesting at first, but proved far too unwieldy and unattainable for PC use.
SR3 had Cyber-zombies.... but they were similarly unwieldy and out of reach of most players. Even if you
were made into a Cyberzombie and accepted the extensive drawbacks, you were still far better off NOT going for cyberlimbs.
Either option wasn't really helpful, except in a couple rare cases for interesting NPC encounters.
I still love my cyberware, and would love to create my own version of Adam Jensen for example.... but with the current rules, a ganger with muscle augs and brass knuckles would punch through a wall far more easily than Shadowrun Adam Jensen and his cyberlimbs. Oh well