Okay I've been over this too many times.
Crossbows have 1-2 range. On enemy phase, right? So Archers can make use of them until the double bow. Right? With me so far?
If you make a kill on your own phase and switch weapons with an Archer so he equips a crossbow, then he's cool with it. Shinon would probably do like 20 per turn due to the fact that he doubles, which is way better than standing there like an ass and taking it.
Or you can use it as a finishing blow and keep it equipped during the enemy phase.
Also, Beastfoe/Dragonfoe + Crossbow = RAPE RAPE RAPE RAPE RAPE RAPE RAPE RAPE RAPE x10000000 because it gets like 84 might that way.
They're not useless.
And by then she's kinda... useless. In relative terms. Uh no? Leo's not doing that much damage to get the kill EXP all the time.