I have used these before for the hell of it after i found them using scavenge. Every time an arrow hit succesfuly the mob would get the status effect:weight. If these are the hidden effect, these would help SO much in BCNM and CoP missions such as 2-5 with the mammets. JUst wanted to say what I myself have observed.
Maat does not buff to what you have equipped. He never did. His level is not influenced by yours, and you can't make him weaker by entering the BC unequipped. Its a myth. Take it from someone who has defeated Maat twice. Once as RDM and once as WHM.
Um...as with all the other gear that SE puts into the game that has horrible stats such as this, i would say that these arrows are to help w skillups and other such things where having worse than base skill is helpful