Shackle vs Havoc for M!Loki

If I intend to use her exclusively for AR-D, do I get Spd/Res Shackle or Spd/Res Havoc for her B skill? Havoc covers a wider area (the entire map vs closest foes+2) and inflicts stronger penalties (-14 Spd/Res vs -8), but PM1 and Fehology both recommend Shackle.

Am I mathing something wrong here?