I do have to point out that the book this is coming from may be a sticky point. They have changed a lot of the lore for caster type stuff since 1.0. The book being referred to is from a time when Conjurers had all the elemental magic (and when elemental weaknesses were actually a thing mechanically). Back then, Thuamaturges didn't have elemental magic at all, they use Astral and Umbral spells. While we can still see vestiges of those days in the current game, we do have to remember that all of that got practically thrown out from a lore stand point. This happened in 1.0 when they shifted how magic worked for CONs and THMs. Long story short, that book may have been effectively retconned as lore. Possibly when they changed magic in 1.0, but most certainly when ARR started up.
Which element tops which is no longer a thing, and I am not sure there is a book around that says that it is now.
Which element tops which is no longer a thing, and I am not sure there is a book around that says that it is now.