I strongly disagree. Mormons are the most Catholic-like non-Christian religion. They accept the validity of the Early Church, but claim that the Church fell into total apostasy.
This is not much different than many protestant versions of Church history, and can be dealt with using the same approach - but it is even easier. Most protestants who value historic authenticity will claim that the Early Church was really protestant in theology, but this was suppressed (but practiced in secret) for many centuries, only to reemerge with the protestant rebellion. This is a complicated claim to refute. While this claim has absolutely no basis whatsoever in history, a secret practice might (by definition) have eluded notice by historians. The fact that the people who invented protestantism (Luther, Calvin. Zwingli, etc) never alluded to such a secret lineage (to establish their historic authenticity) just goes to show how good these people are at keeping their secrets. It’s hard to argue that historic secrets are false simply because they are not clearly established in history.
But the Mormons will have none of that secrecy nonsense. They claim flat-out that the Church gradually fell into total apostasy as a matter of open historical fact, citing many shameful episodes in Church history (the Cadaver Synod, the Rule of Harlots, etc).
As an exercise to the reader, I will defer expressing why “gradual apostasy” is impossible, or why the historic events used to support this claim do not actually support it.
But, at least, Mormon doctrine offers a field upon which to debate doctrine. We begin with the same premise (that the Early Church was valid). The real issue is the question of total apostasy, which is Apologetics 101 for many Catholics on this forum.
Now - Jehovah’s Witnesses are a whole 'nuther story. I spent two years trying to figure out WHY they believe what they believe. I spent a lot of money buying various Watchtower publications, to no avail. Whereas I do not agree with the Mormons, but I can understand their position, I am absolutely unable to comprehend the position of the Jehovah’s Witnesses. I
know what they teach - but I am at a complete loss to
understand why any rational human being believes it. I perceive their theology as intellectually vapid - utterly devoid of common reason.
So, I would argue that among the quasi-Christian movements, Mormons are the best. Jehovah’s Witnesses are the worst.