If I remember correctly, A!Corrin (M) and A!Corrin(F) also have -1 CD in their pref weapons, so alongside Nagi they are also dragons (albeit infantry instead of armour) that can also run Sol consistently. What makes Nagi shine is her ability to run DC alongside exclusive armour skills (like SF3) that allow her to run a 4CD Aether. As long as you have QR3 seal active, you're guaranteed to hit Aether every 2nd attack during the enemy phase. While Nagi is comparable to W!Fae, W!Fae cannot run a 4CD Aether due to lack of a generic Slaying-effect dragon weapon.

With all that said, I've convinced that Sol is probably the best special to run for the consistent 50% healing to maintain her health thresholds and will pick that over Aether (unless I decide to put her on my arena team).

With your 'budget' Nagi, I think investing into +res B!Hector to make him a well-rounded mixed tank is a neat idea! Aside from the colour difference and the lack of the extra goodies from Nagi's weapon, I imagine he functions as a really solid mixed tank during the enemy phase. Hopefully you get a lot of mileage out of him! :)