It's not like increasing duration on these buffs would break blu either.
Here are all the buffs that have duration/recast/set point problems. If all these were to be fixed, I STILL don't think blu would be unbalanced.
Cocoon: That defense helps but still wouldn't use a blu to tank serious VW NMs even with a duration boost.
Triumphant: Even with the attack bonus, the 2h jobs will still do more damage. Increase in duration would push blu slightly further and may even be useful to diffuse.
Barrier Tusk: Already inferior to phalanx until an extreme amount of damage. The cast time AND duration makes this utterly useless. This would find a little bit more use if it had its duration up to 3-5 minutes.
Feather Barrier: This would help in abyssea, but blu is already really sturdy without it. Not to mention no spell traits are attached to this. I think I only set it once because I wanted to see what it did, only to take it off because of how incredibly short the duration of this buff was.
Warm-Up: The duration on this thing is something they got right, but making it take 7 seconds to cast and 4 blue magic points to set? Doesn't even make a good job trait to set either.
Plasma Charge: 5 set points, 60 seconds, 3 second cast. Everything is wrong with this one. Buffing this would not make blu break any sort of balance.
Reactor Cool: Almost got this buff right if only it was 3-4 minutes and much less set points. (3 points seems good)
Amplification: Not only the recast is greater than the duration on this, the gain from this buff isn't that significant to justify using 3 set points and taking 7 seconds to cast it.
Memento Mori: Recast is 4x the duration of this 4set points buff. 20mab would be great to diffuse on mage parties but the duration of this is so bad that I rarely consider even setting it. An increase in duration may also spark an interest of blu nukes.
Saline Coat: This one is one of the few buffs that is decent. Seeing either an increase in duration or lower set points would be great. All this does is add survivability for blu.
Zephyr Mantle: This is one of the few spells that I think its casting time should be reduced. Make it 4 or 5 seconds (Equivalent to utsusemi: ichi).
Regeneration: This one is not bad, but seeing a duration increase would be great as this is already weaker than non light arts Regen II.
Orcish Counterstance: Recast is greater than duration. 5 set points. Pairs with other useless and point hogging spells to create counter. This spell is so useless because of the duration. Even 3 minutes would still make this barely useful because of other things holding it back.