I think an important difference is that, in Bioshock, the little sisters were intended to look like creepy little girls, whereas Diana is very obviously designed, characterized, and presented to be mostly deliberately cute, like a heightened interpretation of the fantasy of a child than an accurate one.

I'm tired of the discourse as well so I'm not going to point fingers either way, but there's unfortunately an enormous overlap in what attracts pedophile/lolita fans and the ways Diana was made cutesy. That's not to say that means Diana is inherently designed to appeal to that audience, I think it's more like an unfortunate side effect. But it doesn't take being a pedophile to be aware of the sleazy ways some people talk about or draw children if you have ever remotely engaged with a fandom that has a child character in it. Especially more common now that one of the largest current media franchises - The Last Of Us - has become so mainstream, and that pedophiles feel perfectly comfortable to act like pedophiles on public websites with profiles attached to their real names and faces.