Well, duh, no one other than JWs are preaching the WTS doctrine. Just like no one other than Pentecostals are preaching Pentecostal doctrine, no one other than Baptists are preaching Baptist doctrine, etc. The "who else is preaching" is such a circular, idiotic argument, I can't believe people still fall for it.
And one more thing. It's been my experience that JWs trot out the ol' "who else is preaching" canard when they're backed into a theological corner over something like 607, 1914, false prophecies, or other wacky, hard-to-defend WTS doctrines/practices. The line of "reasoning" is 'maybe we have some theological issues, but don't worry too much about those, God will correct them in time if they're wrong...and anyway, who else is preaching?'
The WTS teaches that some group has to be fulfilling Matt. 24:14 right now, because the Last Days are right now, having started in 1914. However, what if 1914 is wrong and we aren't in the Last Days? In that case, the "preaching work" of the WTS is not fulfilling Matt. 24:14 any more than the "preaching work" of the Catholic church in the 1300s was fulfilling Matt. 24:14. Put another way, the WTS argument that its preaching work makes it God's only true organization rises and falls with 1914.
So, when a WTS follower concedes Last Days doctrinal issues such as 607/1914, but attempts to prop up the WTS using the "preaching work" argument, the logic breaks down. The "preaching work" argument depends on 1914.