Even if we were to accept the article's summary of Mormonism and orthodox Christianity, all that it has established is that Mormons are not orthodox.
Scanning the article quickly, I did not see a definition of the word Christian as the author is using it. (Perhaps I overlooked it.) Nor did I see any mention that the word is used in just a few places in the Bible, where it appears to be synonymous with disciple or follower.
The author's argument seems to rest on several dubious assertions. One is summed up in the phrase "the Bible teaches" (which appears ten times by my count). The Bible does not teach anything; it has to be read and interpreted. The author seems to believe that just one interpretation is possible.
Another dubious assertion is that Christians believe the same things. The author actually writes about "the common gospel believed by all orthodox Christians through the ages regardless of denominational labels." Considering the history and present state of the broader Christian community, that is nonsense.
A third assertion is that the orthodox Christianity that the author describes is solely Bible-based. However, some of his points depend on extra-Biblical beliefs. For instance, the doctrine of the Trinity was developed much later than the Bible.
At best, the article can be read as an attempt to define, not Christianity, but orthodoxy. Whether he is successful in that attempt I will leave to others to decide.
It would certainly make the discussion easier if we were all on the same page about what it is that the Mormon Church teaches.
I think we have a winner on post #39! To which I might add, orthodoxy is always changing depending on who is doing the defining. F'rinstance, John F. Kennedy's view on tax cuts and military spending would be considered highly unorthodox in today's Democrat Party. He would either be a moderate Republican or an outlier like Joe Lieberman in today's Democrat Party.