Actually, both Mormon and Jehovah’s Witness christology is even more debased than what Arius taught. Arius’ summary of his own false doctrine was “There was when he was not”, “he” referring to the Son. The modern interpolation of [a time] actually further debases Arius’ view: Arius regarded the Son as the first created, but like the Orthodox Fathers regarded time as having been created. Thus to Arius (and real full-blown Arians), the Son exists prior to time, but is not understood as is the right belief to be Co-Eternal with the Father and the Spirit.
Both the Mormons and the JW’s could summarize their beliefs about Christ with the interpolated version of Arius’ dictum as “There was a time when he was not” — making time into a prior creation. (And Mormon triadology is even more screwed-up, though nothing new — it’s essentially gnostic.)
Actually, there haven’t been many new heresies since the 14th century. The only one I can think of is the heresy of the “Name-Worshippers” from the early 20th century (though with a bit of consideration anyone with spiritual discernment could have seen that one lurking in the Evil One’s quiver after the resolution of the Palamite controversies, since heresies always come in matched opposing pairs, and the matched opposite to Barlaam of Calabria’s rationalistic denial of the Uncreated Energies hadn’t manifested itself until about 1913, when hey-presto, some adherents of the Jesus Prayer managed to fall off the royal road on the opposite side.)
Deep post — I need to re-red this