Why play Machinist over Bard?

[Allyrion]

Bard's are pretty much losing their mobility at lv60, so in reality MCH is the new BRD and BRD is the new physical spellcaster.

Gauss Barrel

Equips your current firearm with a gauss barrel, increasing damage dealt by 20%. While barrel is equipped, all auto-attack will stop and all weaponskills will require casting time.
Effect ends upon reuse.

MCH has its own version of Wanderer's Minuet, so nobody is the new BRD.