I'm constantly being told by Catholics that Mormons are actually Protestants. If that's the case, then Muslims must be "deficient Catholics" in funny headwear.
Mormons are not Protestants, but like Muslims, were a syncretist cult based on things circulating in their world. It was a largely Protestant world - but tinged with spiritualism, extending to table-rapping and oiuja boards - and filled with different denominations often led by a self-proclaimed prophet, and influenced by the bizarre psuedo-Islam that the Masons and others adopted in their rituals, mostly because they regarded this as conflicting with Catholic practice.
As a syncretist cult dominated by its founder (its “prophet”) and descendants from his family, Islam adopted things common in its world: the Jewish concept of God, combined with Jewish ritual law; various forms of heretical Christian belief about Our Lord; and paganism and tribalism.
Mormonism adopted features of Protestant Christianity, but there is no way that Mormonism as it is currently constructed can be considered either Protestant or Christian, strictly speaking. Presumably at some point, its president will have a dream and drop the more bizarre things, just as Mormons dropped their anti-black laws, but until then, it’s not really a Christian religion.
It has the same relationship to Protestant Christianity as Islam has to the God of Abraham. That is, there’s a vague connection out there and they are superficially the same in some ways. But it’s very superficial, and this could be useful only in the sense that it might give orthodox Christians an “in” and a better chance to talk to the Mormons and help them get in line with orthodox Christianity.