How about if each primal is assigned a stat. You can build your character then however you want. Each weapon is the same in the sense as "Ifrit is the best primal weapon!"

Ifrit: Fire damage + +STR
Shiva: Ice Damage + +PIE
Titan: Earth Damage + +VIT
Ramuh: Lightning Damage + +INT
Levi: Water Damage + +MND
Garuda: Wind Damage + +DEX

If you are a BRD, you can use either Ifrit's Bow if you want to build your BRD for Damage, you can also choose Garuda's Bow for the added DEX, or you can use Levi's bow to improve your songs. There isn't one uber weapon that you use over the rest. Pick the weapon that mirrors your play-style, or pick a weapon that might improve your weakness.

Been awhile since I played, I think BRD used PIE too, so they could also use Shiva's bow as well. Obviously, we don't know how the stats will be changed, but hopefully you get the idea.