I'm using a fairly old account so I don't have Bashira (though I was lucky enough to get Nanaly but couldn't CC, no black spirits), thus I had to make do with Soma for the longest time and god, other than the low UP cost she wasn't very useful as I would often watch flying units just pass through laughing off her shots. So in my side of it, Spica was VERY important, as alot of my archer-dependent ventures would end in abject failure otherwise.
Any case, like everyone else says, tactically she can boast a slightly larger range and I've noticed she actually has a light form of MR which I guess places her above Nanaly in survival (barely) and strategically her AW passively buffs archers in general so at the least having her (even if not using her) may be worth considering.
I...don't think that's being helpful...maybe archers in general were a poor choice for that event in particular? If that were the case, no choice of archer would be particularly valuable.