Each job will retain the weapon of their class i believe. So if bard gets ranger, it will probably (to my own relief) be a bow-wielding class.

That said I just had an idea pop into my head today.

What if, bother Musketeer and Archer, get Ranger as one of their job options.

An Archer (30) Musketeer (15) becomes a Ranger but has Archer skills as core, picking up musketeer cross class skills.
While a Musketeer (30) Archer (15) also becomes a Ranger but with Musketeer skills as core, picking up archer cross class skills.

While an Archer and Musketeer will probably play differently, the Ranger job can be designed such that the 5 Ranger skills benefit both Archer and Musketeer.

And in the game, Rangers will be the masters of long ranged physical damage. The wear the same Ranger Artifact Armor, but some would be using Bows while other use guns.