If she had reached adult emotional maturity sooner during those 4 years, she would have become just like any other adult on the show. Her significance as a "unique" character would have ended, resulting in a different performance by Ryan.
This is true, but I'm looking at it from the character's perspective. Seven was a combination of a brilliant adult who had access to an incredible store of knowledge. But emotionally was a whole different thing. Because she was biologically adult, people expected her to think and act like an adult. But emotionally, she was still growing up from that 6-year-old who was assimilated.