Walaikum salaam,
While upholding the interpretation used for the relevance of the theme of the article, I don't disagree with your deeper rationale. I think it is quite plausible given that the root of Shajara is well understood as a matter of controversy / disputation. Also, I do not disagree with nouns developing from verbal roots.
I also keep at the helm (as I have argued before) that Quranic terms must be first appreciated in the context they have been narrated and how the primary audience would have most likely understood them. As you know, Arab Jews and Christians would have already had an understanding of this narrative and what the 'shajrah' meant given their interpretations of their scriptures for over a 'millennia'. So is the Quran attempting to offer a newer, better, more corrective explanation? or is it, as the Quran often says it is 'musaddiqan' (confirming e.g. 5:48) an aspect / aspects of an existing one? Personally, I might lean to the latter on this particular case.
However, while staying conscious of the advice in 3:7, I absolutely believe there are many deeper meanings to terms and I am fully cognizant so as to appreciate them given their merits. Therefore, as mentioned before, I don't disagree with your opinion (very plausible) while upholding the relevance of the literal rendering for the purposes of the article.
Your brother,
Joseph.