The 1837 edition accidentally introduced greater in place of great in the phrase “a great curse”. The comparative doesn’t really make sense here since there is no reference to any other curse, only to the destruction of all the people (in Ether 11:1 and Ether 11:5). The 1920 LDS edition restored the original reading, apparently by reference to the 1830 edition. On the other hand, the RLDS text has continued to maintain the secondary greater even though the printer’s manuscript reads great. Elsewhere the text refers to “this great curse” (Alma 30:53), “the great curse” (Helaman 13:18 and 3 Nephi 3:24), and “a great curse” (Ether 14:1) but never to the comparative “greater curse(s)”.
Summary: Maintain in Ether 11:6 the original reading, “a great curse”, the reading of the earliest textual sources (including 𝓞).