I kept on reading, hoping to find a thesis at some point, but alas. The rest of the book seems to follow the same structure as Parsons's introduction -- 2 chapters on Tolkien, 2 chapters on Howard, 1 chapter on Siegel (switching things up there!), and a final 6-page chapter "discussing" their inheritors. The so-called "Conclusion" of the book is literally only a paragraph long and says nothing substantive. Worse, the individual chapters are either biography (no original research, btw) or plot summary, interspersed with the occasional comment or citation.
Given that the title is the only hint of a thesis, let's look at the problems that offers:
- Parsons actually focuses on three writers, not two, as the title implies.
- The title mentions the birth of modern fantasy, which sounds promising, but Parsons makes absolutely no case for why he picked these three writers as the birth of modern fantasy but not others. His major seems to be, "These are major writers of the 1930s," fitting Tolkien into that decade because he conceived LOTR during that period. But there's no mention of Wm. Morris or Lord Dunsany, or those critics who locate the origins of fantasy in the 19th-century Romantic movement of the 18th-century theories of the sublime or antiquarianism. He mentions Lin Carter once without noting his contribution to the Ballantine Adult Fantasy Series, which might be the real birth of "modern" fantasy.
The book is still too new to have gotten any reviews, but I'll be interested to see what is thought by people who forced themselves to go through the whole thing carefully.
Off the top of my head, this is the second book I remember reading in the Critical Explorations in Science Fiction and Fantasy series by McFarlane publishers, and it is the second book in that series that has left me feeling distinctly underwhelmed.