His argument depends on his very unconvincing assertion that Revelation was written before 70 AD. If one accepts Revelation was written approx 95 AD (the conclusion of the vast majority of those who have researched the issue) it falls apart. Nero had been dead aroud 30 years by that time and had been followed by emporers (Domitian) who were much more prolific in their persecution of the Christians.
It is a no less credible assertion than the one which places Revelation in the mid 90s. Gentry's thesis is sound in many respects. The later date is built largely on the second-hand testimony of a single church father as recorded by a single church historian a few centuries later. If that is convincing to you, then I'll not try to suggest otherwise.