If you can create a definition of Christianity broad enough that Mormons could be considered Christians, then that definition would likely be broad enough for Muslims to be considered Christians. If you have to water down the definition of Christianity that much, then what does Christianity even mean?
Muslims don’t consider themselves Christian. And Jesus isn’t at the core of their religion (even if he is an end-times messiah)
I think you could make a very good case the Jesus isn't really at the core of Mormonism either (Adam-God doctrine, Law of eternal progression, Elohim vs Jehovah, etc.) Especially early form of Mormonism (less so in recent years as Mormons have made a concerted effort to pivot towards a more Christian appearance and public persona within the last 50 or so years).