It is really pretty simple:

1) For coil and ex primals: BRD>ARC
This is really summed up in the fact that your extra utility really can't make up for the added DPS loss, and the fact that if someone dies, it is much more serious in this content. Plus your songs are absolutely invaluable in any fight that lasts longer than 4 minutes.

2) For ALL OTHER CONTENT: BRD ??? ARC
For all of this content, gear is so ludicrously overpowered that the content is trivial. It really doesn't matter what you do here because the content is so simple that it doesn't end up making a significant difference anyways. If you like playing archer, then go for it. Casual content is meant for fun anyways, not serious play.