Kin37ix said:
Things die too quickly, things need !! proc, we have Dia II, and we lose points in other stuff if we choose lol Dia III.
An extra 4% Slow isn't exactly groundbreaking, throughout the course of a fight it'll save maybe a handful or two of shihei. The same can be said for Paralyze.
I don't find Phalanx useless either, FC burns for one, and as a MNK the only real "defense" you can have is PDT/Phalanx due to Counterstance. Dia 3 is quite useful for a lot of Heroes NMs/parties with too many lower levels since they have rather high defense, and benefits every DD not capping pdif.