"His" main critique is against evolutionary theology which is common amongst reformers and Christian critics. "God was seen this way. Then it changed and he was seen this way. OT God is angry. NT God is compassionate etc" This is not a new idea and has been held by the Orthodox church since it's inception and has been codified for the last 1200-1300 years. The Orthodox view everything consistently through a Christological lens which is why their view of sotieriology etc is so different than what you will get from Protestants or even Roman Catholics.

Fr. Stephen De Youngs book is just a readily consumable encapsulation of ancient arguments, historical findings (such as the Rosetta stones) with his own analyses and contributions. Would you be better off reading the church fathers and primary sources yourself? Possibly but you'd also need to know ancient Greek and Hebrew.

Christians and academics love to argue and I'm not surprised to see that people are critical of the book. I don't think there is any religious commentary that hasn't received criticism.

At any rate I encourage you to look at Orthodox theology more generally. You will find a logical consistency and depth of analysis that the secular world usually says is lacking in the Christian worldview.