Noumenon:
I guess what I have in mind that some in the 7 Churches did hold to beliefs or teachings that were contrary to Christianity. For example, in Pergamum: "You have people there who hold to the teaching of Balaam..." that led to idolatry and sexual immorality....."Likewise you also have those who hold to the teachings of the Nicolaitans." In Thyatira, it is said: "You tolerate that woman Jezebel who calls her self a prophetess. By her teaching she misleads my servants...." etc... These were not minor infractions. These endangered the entire church. If this was the state of the churches in John's time, I think they become a very good picture or symbol of the state of all churches today that claim to be "Christian." Churches who profess Christianity come under the authority of Christ. And by doing so, they eventually come under his scrutiny and judgement.
While I think that Jehovah's Witnesses probably do have "the truth" on doctrines like trinity, soul and hell, I think their major mistake is substituting their organization for Christ. For example, the organization teaches that salvation can only come through itself. (Savior?) It implies that people are redeemed by their ministerial works. (Redeemer?) It criticizes and judges all others outside the organization. (Judge?) These roles are Christ's alone. This, in my opinion, is a major error made by the Watchtower Society.
It has only been in recent publications, I understand, that the Society has begun to emphasize the importance of Christ. And this could be a reaction to the criticisms of others who noted the secondary postion that the Society relegated him throughout the years. I remember one young JW woman who said "all the churches talk about is Jesus, Jesus, Jesus." I remember how shocked I was to hear this. I always thought the "gospel" was all about Jesus!
So, I would never use Jehovah's Witnesses as a measuring stick to guage other religons. It was once said "a little truth is a dangerous thing." Yes, I do believe they have "a little truth." But just consider how they have used it to abuse other Christians. And if Christians are found in the other church systems, think of the implication of Jesus' words: "...as you have done it to one of these least ones, you have done it to me."