Allow me to preface this by saying, I am not Arian. But I have done my due diligence in studying Arian (not necessarily Jehovah's Witness) materials. There's actually two different "constructs," or "models" (if I may use the term fluidly) which are attested in Arian circles. In order to know how to interact with the appropriate model, one needs to be able to recognize the difference between the two. Even in Arian camps, the two models will get confused or conflated, when in reality they differ.
- In Model A, Christ "came into being" simultaneously at "the beginning" (Gen. 1:1).
- In Model B, Christ "came into being" at a time that antedates "the beginning" (Gen. 1:1).
So yes, Jn. 1:1 would be an appropriate "rebuttal" against Model A; however, one needs to be prepared to deal with this view's standard interpretation of Jn. 1:1. Essentially, they try to suggest that Christ had His "beginning" at "the beginning" of Jn. 1:1. But, as you have suggested, there is an element to this that suggest that the Word was already existing prior to "the beginning." And so does every other text which speaks of pre-existence, 1 Cor. 8:6, Col. 1:16-17, Heb. 1:10-12.
Model B is probably the construct people should be geared at offering a rebuttal to. Proponents of this view would agree that the Word was already present prior to Jn. 1:1 (cf. Gen. 1:1), but that the Word was created at some point prior to.
I think both models are quite flawed, but if one is going to interact with "Arianism," then it should be geared towards interacting with Model B. Both models have quite a bit of problems, and adherants of both models do interpret specific passages much differently. This is an area I have spent quite a bit of time in.
If we don't hear back from CorrectiveLens, I'd be more than happy to go over some of the passages that you may have questions on. We could probably arrange to even do it via Skype or something, because with the appropriate visuals, I think it will help bring out the "difficulties" with their suggest interpretations and help "bridge" the ones I attempt to make. Don't let them act like they don't have problems; oh, because they do. They just don't talk about them, and no one has vested the time to really dig their heels in to interact.