I think this is good, but some of your historical information is off, and that skews your explanations.
For example, Mormons frequently misunderstand classical Trinitarianism, which posits three distinct personages which are one God. Because of this misunderstanding, Mormons typically cite against the trinity things like Acts 7:55- “filled with the Holy Spirit, [Stephen] gazed into heaven and saw the glory of God and Jesus standing at the right hand of God. (Acts 7:55 NRS).” A trinitarian who knows his theology shrugs, because s/he too believes in separate personages. The idea then, that Joseph would have been so blown away by seeing two personages instead of one that he never ever could have forgotten or misspoken is based upon a misunderstanding.
Second, it’s absolutely true that LDS usage and perception of JS’ vision has shifted, and in spite of the context I’m surprised you didn’t cite anyone to that effect (e.g. James Allen in Dialogue in 1966, then JMH in 1980.) But you strongly overstate the idea of confusion or competing versions. While they didn’t seem to talk of the account using language as precisely or fully as we’d like, it’s equally clear that John Taylor and Brigham Young *did* teach that JS’ had been visited by the father and son.
For example, John Taylor in 1876 teaches
“When God selected Joseph Smith to open up the last dispensation, which is called the dispensation  of the fullness of times, the Father and the Son appeared to him, arrayed in glory, and the Father, addressing himself to Joseph, at the same time pointing to the Son, said, “This is my beloved Son, in whom I am well pleased; hear ye him.”- JD 18:325–6.
I think you’re offering a great framework, but the some of the supporting data is just as off as what you’re trying to correct.