Personally....I'd give the cat more time to adjust. Some cats just like some people take more time to get comfortable. In terms of the personality you were expecting, with respect I feel that that is a bit unrealistic. Breeders cannot guarantee personality any more than a mother of a human child can. A human mother may want an extroverted child - but way too many factors are outside a mother's control to guarantee this in any way shape or form. Personality as far as i know is always a mix of genetics and environment. Sure, certain breeds have a tendency toward a certain personality but that's all it is - a tendency.
I would wonder if there are any loud noises around perhaps from the street or somewhere else that you are used to but not the cat. I would also 100% have this conversation with a vet as there might be a medical issue at play.
But to me, this cat does sound like it is making progress just not as fast as you want. (It's not hissing anymore right? comes out slightly more often right?) If I were a gambler I'd bet hard that the cat will get friendlier over time.
I hope other members with more cat knowledge than I have will also chime in here.