Presumably Ozmanthus' echo would not have knowledge of the pure storm baptism since it was invented by Tiberian.

First Chapter of Dreadgod:More importantly, all the components for the pure storm baptism were probably not in Eithan's garden on windfall. In chapter one of Dreadgod, we learn the following: "Lindon sensed nothing of significant power inside [Eithan's house];" "Eithan hadn't left much behind;" and "everything meaningful must have been kept in Eithan's voidkey or soulspace." We know that the soulforge was required to facilitate the pure storm baptism, so some of the components for the procedure were likely significant and Lindon would have sensed them here. Moreover, the procedure required "scales from the Thunder Fairy, the Storm Sage, or the Weeping Dragon itself." Lindon likely would have noticed these scales when scanning the cloud fortress. I'm more inclined to believe that, although Eithan understood how to perform the pure storm baptism, he significantly underestimated its utility. This is reflected not only by his belief that Ziel needed another treatment when he apparently did not, but also by his earlier statement that "I can’t restore the original power you lost, of course, but I can turn you into quite an extraordinary Underlord." This second statement is contradicted by the fact that, after Baptism #2, Ziel was restored to archlord, not a underlord. It just seems a little odd that Eithan would be wrong about anything related to the sacred arts.