DC doesn't really work too well on fliers unless you're going to run the whole 9 yards of DC + Iote's for most fliers. It's an interesting gimmick but giving a lance flier DC in the wake of Glyn (even if she's rather whelming) probably isn't the best call.
The best DC users for fliers imo are Michalis and Myrrh (both physical tanks and greens, since common res powerhouses are typically going to be blues and reds are handled by your blue flier/bladetome flier). Budget option on Myrrh is LB Defense+, but DC is great on her.
As I always say, your best options for DC users are:
- Sigurd (basically makes him less effective vs nonbraves & desperation users but the tradeoff is a massive plus considering how much of a tank he is)
- Myrrh (reasons stated above)
- Swordhardt (DC + QR = quadding on enemy + doubling on player)
- Armorwood/Winter Robin (both swift speedy tanks)
- Effie (DC + Berkut's Lance)
- Michalis (res bulk is enough to tank most blue mages and kill in a hit or two)
- Axura (complete blue mage/Reinhardt check)
- Winter Chrom/Lissa (abuse QR/vengeful to it's best effect)
- Oboro/Lukas (ridiculously high investment but immense bulk; Oboro can't defend as hard vs bows but can soak tanks ridiculously well, even with a Slaying Lance+ Res refine)
- Roy (new refine = QR 5)
- Leif/Ayra (another high investment option but they work ridiculously well with Slaying Edge+ and their toolkits having low charge specials at the ready)
There's quite a bit of options, and even with high investment something like Bartre can become a monster; however, I'd say the list above is a good list of DC-recommended units given the rarity of the skill.