Question about human helplessness/prematurity and the imaginary

Lacan often points to the “prematurity” of the human baby as a key factor in the development of the imaginary/Gestalt identification process (e.g. mirror stage) that results in the creation of a stable ego in an individual. This even comes up in Freud in “Inhibitions, Symptoms, and Anxiety” when he refers to “the biological factor…a long period of time during which the young of the human species is in a condition of helplessness…its intra-uterine existence seems to be short in comparison”.

My question is such — is this actually a biologically correct idea? Aren’t there many other mammals who are born “prematurely” or in a state of “helplessness” in the Lacanian-Freudian sense? What about marsupials, who literally are born in a mostly undeveloped state and must be nurtured within the mother’s pouch? I guess my confusion is — if this prematurity/helplessness is such an important factor in the development of the human imaginary and the formation of egoic structures, why does it only happen in humans? I get that humans are different because we have a Symbolic Order/language, but wouldn’t Lacan have said that these structures at least partially form because of humanity’s helplessness-in-infancy?

somewhat of a noob to lacan so apologies if this answer is rly obvious/I’m missing it somewhere in one of the seminars. I do like the idea of helplessness and its connection to the imaginary, I’m just unsure if the biological explanation actually holds…