Well, at least Nanya is accurate on the eye, because if we take Vice's little sister as an example, Mid-Childan medical technology is unable to replace her eye and give her a fake one instead. I guess the eye-pàtch is for(aside of Rule of Cool) further priotection as a fake eyeball could fall from Signum's eye-socket during battle.
And yeah, so far there's no official material talking about advanced prosthetic limbs, i still find a bit strnght that no limbless characters exist in canon specially considering the military setting xDU.
About Laevatein's sheat Signum barely used it as a sword, she uses it more as a shiled or a parrying tool.
You're under the impression that Mid-Childa has Earth-level medical technology, but the fact of the matter its technology is still better. As for prosthetic limbs, we haven't seen any beyond combat cyborgs, which is why you haven't seen one capable of working as a normal one.
And there's little change in her combat style. Laevatein's sheath acted like a regular blade for her as is.
I'm yet to see a prostethic limb capable to work as a normal one in the Nanohaverse(as in, receiving orders of the brain that work on real time with the same speed as a normal hand) but your explanation seems plausible.
About Schlagenform i guess it would be necessary to apply some technobabble or applied plebothinum since artificial limbs aren't that flexible ...or fast enough to make such complex wrist moves. I guess that will take some time and it's why Signum changed styles.
The thing about prosthetics and replacement organs in Nanoha is that they're perfectly viable as just replacements--its if they're made better than they are that they start to fail, and what require combat cyborgs to be built from birth with extreme genetic manipulation.
Signum's new hand in BTF is just that, a hand. She's no stronger with it, and if you read the latest chapter, Shari tells her that since she's not fully acclimated to the hand, using Schlagenform would merely snap it off at the wrist. Which is probably why she's now dual-wielding instead.
I'd just like to point out that the prosthetic hand bit in BTF is not inaccurate according to canon, and is in-fact in line with everything else, especially concerning the whole combat cyborg thing that brought the issue up in the first place.
Ripping? for giving extra points of view? You're treating me like if were all "AHH THIS FANFIC SUCKS!" I just thinked a bit more deeply on the details of certain scenes and posted accordingly. The moderators reguled my spelling which i'm glad for and also moved the incresing exchange of opinions to the proper section(Fridge Logic).
Maybe i should move "A fate worse than death" to YMMV? It's a bit sibjective now that i think of it. But for a warrior, dying in the battlefield is the maximum glory, surviving maimed is like being death in life, so i think it applies.
Hell-bent on hating it? I think that's a bit of an exaggeration, sure there are parts that i don't like about that fic(fanservice, scrambled power levels, characters acting deliberately careless for the sake of a plot twist). but i admit Nanya is good at making atmosphere when things get serious.
Even if i at first naturally disliked what happened in Ch. 46 i admit it have some potential(in fact, it reminds me of one of the possible developements for Signum i proposed about a year ago of getting her crippled and descend slowly into darkness victim of her own impotence). I still don't know what he has planned yet so i'll wait and see i guess.
Hard to admit but, some of his chapters are an entertaining read sometimes.