I have heard Mahesh speak over several days at a conference in the UK in 2002, and firstly he is not American in origin, didn't grow up in America. He is Indian and won a scholarship to do post graduate studies in America, although he may be a naturalised citizen by now.
I found him to be a humble man, and his emphasis on the miraculous is because this is his life experience with God, and I also saw people getting healed during his time of teaching. I believe God uses him to teach the Word, and facilitate personal transformation in people's lives. He gives his personal testimony and speaks of what has influenced his own walk with God and one has to therefore put what he has shared into this context.
It is unfortunate that just because he doesn't give a comprehensive history of fasting according to all mainstream churches, and you are disappointed regarding this, that you would put down the incredibly positive and encouraging message in this book.
That is not what this book is about. It is an encouragement and teaching to promote the practise of fasting in one's own life, especially for those 'new' Christians, or those Christians who have not previously practised fasting. Many people do not have the privilege of a life long nurturing with the practises and teaching it brings in a church.
I have also had the privilege of hearing Derek Prince speak on fasting many years ago, not sure if he has written anything about it but you could research this as his teaching was excellent. Derek passed at the age of 88 to be with the Lord. I would also recommend "God's Chosen Fast" by Arthur Wallis.