Want to upgrade Sprint Shoes but if upgrading won't increase the duration of Haste right? All it does is improve what you receive if you dismantle them.

Start attacking from (your) left to right (Right Pauldron -> Left Pauldron). Keep Decimation set until all your party members have shell, then switch to Diversity and continue attacking from (your) left to right. This is because the Left Pauldron deals water-based damage, which your party will be most resistant to, giving your medic an easier job. Keep attacking, switching back to Decimation when shell wears off, and then back to Diversity. Be sure to only use these two paradigms as all the enemies attacks will be focused on one party ember at a time and you'll end up getting caught out without a medic. Barthandelus will cast Enchanted Veil (shell and protect) and Mystic Aura (Faith and Haste) on his armor during battle, you will just have to put up with it (with no sabetour). As I've said earlier, Barthandelus will increase his magic power, using Magic Amplification, periodically (every minute or so) so this is why you should focus on one piece of armor at a time, eliminating as many as possible before he reaches third level magic attacks. By this time only the Left Pauldron and Ailette should be left, dealing lightning and water damage. This part of the battle should only take you a few minutes.