SBF - Mormons did an analysis of their figures and concluded the Internet was not an important factor in growth or decline.
I would like to see their reasoning.
When it is said that the internet is not the only factor, do they mean that apostate sites are not the only factor, or the internet in general. Whilst apostate sites have limited reach, the Internet is critical to the collapse of Watchtower and religion in general.
There are a range of factors in addition to apostate sites. The generation changes since 1995, 100 years of no-show from Jesus in 2014, porn and the relaxation of attitudes to sex, the rise of acceptance of homosexuality, finding support groups through social media. Each of these have some relationship to the internet and access to information in general.
The decline of religion in general is largely to do with information, which is being more and more rapidly dispersed due to the internet. There are two areas that information helps, the shrinking God of the Gaps due to Science, and the realization that it does not make sense to say God resides in only one religion, when religion affiliation is mostly decided by one's place of birth.
I don't know how it would be possible to work out how much affect each attribute has to the overall decline of Watchtower, but it needs to be recognized that the internet is tied very much to so many of the reasons for declining growth.