No I am Catholic. I am not defending Mormonism. I am merely pointing out that historically Arians and various other heretical groups were considered Christians by small-o orthodox Christians, so it is rather odd to claim Mormons are not Christian because they reject the Trinity given this history.

Please note that Latin Christians in the early medieval period were rather bemused by Greek Christian attempts to define precisely the Trinity and the Incarnation, thinking that such philosophical hairsplitting was not worthwhile. As they were having far more contact with the Arians, perhaps what was going on was more a cultural split than a question of theology.