The Chosen Ones

It makes sense if you compare fradz with tharo, their power differences are enormous, so i think fradz shouldn't be a 5th ranked, a 4th ranked maybe. What did you mean by delicate skills of shadow? Fradz can become invisible, but i don't think it's a "delicate skill of shadow" (considerating him like a 4th ranked).
I think Phodom is more strong than we think, but not strong enough to be a 5th ranked...
Galeoth maybe can't control another element(and i still angry how could a ice mage almost freeze to death)but galeoth manipulates water and ice with a ability that is far stronger than many magics in game, (i still don't know from where the magic hammer came from though), i don't know if ice and water are the same element, but still we can't say for sure that just because you mastered a element it'll now unlock a new element (yes, i think you're wrong about this black).

Another thinks we have to considerate are the exceptions:
-Tharo is a exception of exceptions, he's just too strong and to mysterious
-Fradz has a far more potential than Tharo(because of ... Fradz), but he still not that strong(yet very strong)
-I think Phodom may be a exception too, maybe he's stronger than many 4th ranked, but yet weaker than 5th ranked.
-In my opinion, Galeoth isn't thaaat strong considering he's a 5th ranked, of course he's stronger than any dragon slayer under him(theorically), but i think as a 5th ranked he is kind of weak.

Another observations:
-The difference between a 3rd -> 4th looks like enormous, and 4th -> 5th, looks like even bigger(of course the execeptions may break these rules)
-Galeoth is more famous than strong(like you guys said) and he's friendship with the king maybe turned him into a 5th ranked more easily(although he deserves it)to make his dragon research easily



another thing, if you consider the Black's review(that i really liked) there's no