My little BLM is only level 28 so not really even a BLM yet so I don't have first hand experience with this. However, I can see as a caster with long cast times how their DPS would suffer in movement intensive fights. You move, you go to cast, and right before its fully cast you have to move again, happens to me as a healer all the time. Perhaps rather than a shorter cd on Swiftcast an addition of something like AST's Lightspeed would be appropriate here. Its one of my favorite skills AST has actually Its not instant, but it lets you get fast casts off while having to move.