Diamond - I agree with you in part. Is the WT-Russell-Mason connection a theory? Yes. Undocumented though? No, the connections and similarities in imagery, symbolism and even belief structures are undeniable.
Was he actually a Mason or did he just study and emulate them? I don’t think there has been any evidence to date to prove this one way or the other. It may very well be the case that he just studied them as he did the pyramids. And the similarities certainly don’t prove any of the conspiracy theories (Illuminati, NWO, etc…)
Either way, it provides insight into the early years of the WT and further signifies the break between Russell and Rutherford. I really would like to see an example of that exact image in connection with Masons (or wherever it leads).