I haven't actually read it, but the book you're talking about, Heraklia, must be Alfred P Smyth's 1996 book King Alfred the Great. Smyth is Professor of Medieval History at the University of Kent. And yes, he is a respected academic, but the reaction to this book by many experts in the field was somewhat sceptical. I believe some may have thought that Smyth was trying to make a name for himself by being deliberately controversial.

The "character arc" of Alfred as described by Asser is that of an illiterate king who struggled against adversity to build the English nation; who learnt to read and write English and Latin in his middle years. Smyth says that Asser portray's the king as a saint with an unhealthy desire for pain and illness.

Smyth argues that Alfred had quite likely been a scholar from a much younger age, and also that Asser's Life may have been a late medieval forgery - and calls the author Pseudo-Asser. Alfred is the only Anglo-Saxon king whose character seems clear to us, and the one about whom we know more than any other. But much of this information comes from Asser's biography. However, Smyth points out that Asser seems not to have known the name of Alfred's queen, Ealhswith, and fails to mention other detail's of Alfred's court, despite being the king's close advisor and tutor.

Smyth has also published The Medieval Life of King Alfred the Great: A Translation and Commentary on the Text Attributed to Asser. Here he provided a commentary on the whole tradition of Alfredian biography. He suggests that the text may have been composed at the beginning of the eleventh century by Byrhtferth of Ramsey, or one of his circle.

However, a couple of years after Smyth published his biography, another book came out by Richard Abels, Alfred the Great: War, Kingship and Culture in Anglo-Saxon England. Abels concluded that Asser's work was indeed genuine, and has the support of the majority of academics in the field for that assertion.

I would strongly recommend reading Smyth's article Unmasking Alfred's false biographer in British Archaeology no 7, September 1995 for a fuller account of Smyth's thesis.