Context is everything. In the original quote I was more trying to illustrate the growing aberration that is Protestant history. Do I believe that Baptists and Mormons are cut from the same cloth? God forbid. But did the growing uncertainty and chaos that the move further away from Orthodoxy and the fertile soil of the American 19th century Restorationist explosion lead the way for such deception to take hold?
JWs, on the other hand, are trickier. In the beginning they were nothing but another late 19th century Restorationist sect with a strong Dispensationalist current, closely akin to the 7th Day Adventists. That they moved into outright heresy cannot be denied, but are they any less heretical than many of the teachings that are coming from, say, American Episcopalians (not that all Episcopalians have fallen so low, but a growing percentage everyday, and certainly those in the highest seats of power)? For that matter, how would you categorize Oneness Pentecostals? I have heard more than a few Evangelical pastors playing along the precipice of heresy, one slip on the sola scriptura edge and they fall back into early Gnosticism, Manicheeism, or Marcionism.
I am very uneasy with the term cult, by the way. From a certain point of view (and not necessarily a materialistic one) any religion can be labeled a "cult". I've even seen a few sites that would call perfectly Orthodox monasticism "cultic" behavior. Now, for harmful "cults" we have certain ones that can be clearly labeled as such, the Moonies, the Branch Davidians, the followers of Jim Jones, and the like. But the whackiness of Mormonism already played itself out, and the only people endangered by JWs are those direly in need of blood transfusions. Mormonism is these days a sub-Christian religion, indeed akin to Islam, in that they claim Christianity while teaching Paganism. JWs are clearly Christian heretics.