I understand what you mean about the way that Starhawk writes. I think the valuable things in this book are actually the exercises and the rituals. I am fond of this book because it is the first book I read on witchcraft. (it was the original edition not the 20th anniversary edition)
I believe that the legends that she is referring to are the legends of the UK...that is, England, Ireland, Scotland and Wales.
It would be really nice if Witches could claim an ancient lineage and we can in that witches have always been in existence. What has not always been in existence is the current definition of what a witch is...the fact is that time has brought about many changes in all cultures that still exist today. There are those that no longer exist. Change brings new understanding and with that understanding we recognize that what was a witch 500 years ago may not be remotely close to what a witch is now.
Remember that this book was published 20+ years ago, and being a person that has traveled a strange and diverse path of witchcraft I can promise you that things have changed immensely. Most people were still very afraid to step out of the broom closet. I remember the first time I told someone I was a witch...they literally shifted in their seat and leaned back, away from me.
I think the disappointment you are feeling is so very common, it is the realization that really, we are creating the myth, we are creating the legend and we are doing it out of remnants of things we believe happened hundreds even thousands of years ago.
What is different in Starhawk's book is that she points out that this thing that we are all trying to get at is there and has been there since the dawn of man. What we seek is an ancient connection and the disappointment comes when you read through thousands of pages and cannot seem to pin down where that connection is.
The connection is within you, it is within me, it always has been and always will be.
There's a lot of good information in this book but sometimes it gets lost in the mire of her verboseness.
Also, I think this book is more about her own personal experience as opposed to instructional.
Keep reading, and seriously try some of the exercises. The other thing you might try is write out what it is you want in being wiccan and or being a witch. What do you expect to gain from it and give from it ?