Never underestimate the ability of senior academics to dismiss a book with what sound like words of praise.
“Not since Frazer’s Golden Bough, has anyone achieved such a grand synthesis of world mythology. Boldly swimming upstream against the present scholarly emphasis on difference and context, Witzel assembles massive evidence for a single, prehistoric, Ur-mythology. An astonishing book”
–Wendy Doniger, Mircea Eliade Distinguished Service Professor of the History of Religions at the University of Chicago and author of The Woman Who Pretended to Be Who She Was
In other words, I think she is saying that it follows a solipsistic (“swimming upstream”) and out-of-date methodology (the Golden Bough reference), and what astonishes her is that Oxford actually published it.