A bit late to get in on this reply, I suppose, but I'm still going to throw in my two cents as I disagree with the assessment of Agnes. Agnes isn't going to shine until awakening, but given his team composition and how many classes he has pre-CC, having a lv48 necromancer who doesn't need to CC at all makes her a very strong option for single target caster right now. Necros attack slower than witches and don't slow, so you can't really sub her in for a witch, but if he has to work Nenya up from scratch, and has other priorities (like CCing Bashira, for example), removing Agnes is going to waste a lot of ST magic damage potential he already has.
I'd recommend dropping Bernard or Yurina, the dark knight in favor of a witch and keeping Agnes in until you have caster options that are of similar strength. Yurina's old, and as such, the power creep is very weak with her. In general, her cost doesn't really justify her use in most situations. As for Bernard, there aren't many situations where you'll need two heavy armors at once which Katie or Lisse can't sub in for.
In general, mounted archers are weaker than their non-melee counterparts, and most situations where you'll want to use one will be because you're looking to augment your ranged dps. Her skill is nifty, but doesn't really do anything for your team's DPS, so I'd consider her a niche unit at best. I have her at CC48, and I've already stopped using her in favor of Margaret, who is only a gold. (Albeit a really good gold.)