>What you've created is a human.

That's incorrect, for reasons I've already stated. Humans and simulated humans are not interchangeable.

>If a system takes the same inputs and creates the same output it's the same system on different substrate.

You can't feed a simulated human real food, and you can't feed a real human simulated food. You can talk to a human by vibrating real atoms at them, but you need to make simulated atoms vibrate in order for a simulated human to hear you. Clearly they don't take the same inputs, they take analogous inputs. You're still making the error of confusing the literal thing for its symbol.

>You don't say a human stops being a human if you put them on a ventilator, do you?

Inappropriate analogy. You can put a human into a ventilator and you can also take them out. It's impossible to "place" a real human into a simulation or to "take" them out of a simulation into reality. I'm putting the verbs within quotes to emphasize that I'm using the strict literal meaning of them, which is to translate configurations of atoms into or out of a place.

You can "put" a human in a simulation in a looser sense, which is to copy them and put their analogous representation in the simulation.

>How much of the biological human can be outside the meat body before you stop recognizing them as human?

The moment they stop being made out of atoms and are made out of simulated atoms.