When looking at it from this angle, there's really nothing to be said about Mormonism that can't be said about any other religion. All of Christianity is based on a set of claims by a Jewish preacher named Jesus of Nazareth, as documented (correctly? not everyone agrees) by disciples of his, several decades later. Islam is based on claims by Mohammed, Buddhism is based on the teachings of Buddha, and so on.
All religions have their detractors that come up with long lists of things that may or may not be true, and may or may not be cited in any sort of proper context, to try to make that religion look silly to outsiders. The simple truth of the matter is, it's far easier to make claims about someone who's been dead since long before any of us were born than it is to fact-check those claims. How is Mormonism any different?
The difference, though, is that Latter-Day Saints can actually answer that question with a solid "no." The Book of Mormon closes with a promise rooted in a very different doctrine:
4 And when ye shall receive these things, I would exhort you that ye would ask God, the Eternal Father, in the name of Christ, if these things are not true; and if ye shall ask with a sincere heart, with real intent, having faith in Christ, he will manifest the truth of it unto you, by the power of the Holy Ghost.
5 And by the power of the Holy Ghost ye may know the truth of all things.
-- Moroni 10: 4-5
This is the doctrine taught to every person learning about the Church of Jesus Christ of Latter-Day Saints: the ultimate source of truth is God, and He will confirm the truth to the hearts of those who sincerely seek it. A Latter-Day Saint's testimony does not go "I know that the church is true because I know that Joseph Smith was a true prophet," but rather "I know that Joseph Smith was a true prophet because I know that the church is true." It does not rest on Joseph Smith's credibility, but rather on God's.