It seems like you're trying to have it both ways, WorkOver. I'm doing my best to ignore the way you keep repeatedly calling everything and everyone stupid, etc, etc, and just listen to your complaint itself -- and even so, you're contradicting yourself. Calm down, take a deep breath, and read the rules, for starters. You've shown (on multiple forums) that you're not taking the time to read about how things actually work, and you're skipping straight to the complaining and insulting everyone part. Ease up.
Now, the other thing you've got to do is, after having read the rules, to not overthink them. Don't insist the system is meant to be abstract, and then think up a bunch of reasons for that abstract system to fall apart when a dude's throwing a punch. Is it abstract, or is it so realistic that you're bringing in plenty of real-world fighting science for realism's sake? In Shadowrun if you've got an Agility 4 arm (though why you'd stop at Agility 4 is beyond me), and you describe your attack as punching someone (or stabbing 'em with spurs in that arm, or zapping 'em with the shock hand, or shooting them with a pistol in that hand), guess what? You get to use your Agility 4 (though, again, most guys pulling this trick would go much higher, nuyen allowing). That should be awesome. It should mean you've got this bumbling clutz with a really badass combat-augmented arm all full of servos and gyros and stability hardware, capable of acts twice as precise as the stumbling, fumbling, meatbody it's bolted to, and suddenly your Decker is dangerous with a gun in his hand. Awesome!
And yet -- for some reason -- you're acting like that's (a) not how the rule should work, while simultaneously insisting that (b) cyberlimbs are underpowered.
Just embrace the notion that "if you're doing stuff with Limb X, you get to use the enhanced attributes of Limb X," roll some dice, and be happy. It is an abstracted, simplified, way to look at things, but Shadowrun is at it's best when it's being abstract and simple, IMO. Don't overthink it, house rule it, and then call it underpowered based on your personal interpretation; just accept it for what it is, and have a good time.