Mormonism absolutely started as a cult by the first, traditional, broad definition; pretty much every successful religion and denomination started as a cult, based on the standard definition. Even the word "culture" gives a nod to that simple fact. Frankly, we collectively overuse the term "cult" so much in our modern society that many people have lost the ability to distinguish between the definition above and the more sinister definition that includes explicit mind-control, brainwashing and coercion.
Having said all of that, it is possible for individuals within any organization to lean toward the more sinister definition of culthood. Thus, my favorite introspective response ever to the question of whether the LDS Church is a cult is:
"Lord, is it I?"