Not to defend it, but she rarely whispers, I can only remember a couple instances, and it's in emotional moments so it's kind of like she's screaming whatever she's signing. And they do show the stump, just not bare, she's wearing a sock thing over it. And she does walk awkward for a little while after her prosthetic leg breaks and her tinkering grandpa makes her a temporary one.
It does, but it's expensive. Like, sure there's Winter Soldier's arm, and in the now canonized Defenders shows, Misty Knight gets her cyber arm after she gets amputated, but it's like a multi million dollars prototype given to her by Iron Fist, who's not quite as rich as Stark but still a billionaire who owns a huge tech company.
Kingpin is rich but not rich enough to give her a cyber leg back when they were in good terms, and during the show she's running around solo and getting her shit repaired by her small town pawn shop owner grandpa. Not quite gonna have Wakanda tech in there.
Plus they want to keep the prosthetics reasonably realistic so the cripples can feel represented. "I, too, have a leg like that, I too can be an ornery unlikeable psycho bitch".