Novus Weapon Cost

[Mcshiggs]

Each item converted has a 1 in 72 chance of giving the correct type materia

The odds are better than that, like battle gear won't give crafting or gathering materias, plus the item level of the gear also determines the grade of materia you get, and the type of battle gear you are assimilating can rule out some materias as well, like DoW robes shouldn't be giving materias like quickarm. Depending on the level it is at worst 1 in 36 and gets a bit better when you have DoW or DoM only gears.