My understanding is that the baby, equipped with only instincts / biological hardware, is hyper-aware of the raw emotional communication of their caregiver.

It's this really raw, basic emotional experience which shapes our "core" understanding of ourselves and the world we live in.

"Healthy" attachment in this early stage comes from the caregiver being able to regulate the emotions of the baby. If the baby doesn't feel connected to the caregiver - such as if when the baby cries they don't receiving loving reassurance of their safety - then they form a dysfunctional template for social attachments and poor emotional regulation ability.

If the random babysitter has consistent and parent-like loving connection with the baby then maybe you're right, but I doubt that's the case.

This is really wrong. My baby already recognised and was soothed by my voice and e.g. quieted in my arms much faster than the grandmother's at 2 months.

Research apparently indicates that being loved in your first year is key to your development.

Is your doubt founded in any research or more of a gut feeling?

We hope for "a 3-year-old child who is running, jumping, telling stories, making friends, and learning to read."

It could also be biting, jumping off of tables, hiding poo, poking holes in drywall, poking both ends of the dog, hitting sleeping parents with tools, and learning to scribble in books.

Children are haughty, disdainful, quick to anger, envious, curious, self-seeking, lazy, fickle, timid, intemperate, untruthful, secretive; they laugh and weep readily; the most trivial subjects give them immoderate delight or bitter distress; they wish not to be hurt, but they like hurting others: they are men already. – La Bruyere, Characters (1687)