I have 2 Sabers, which I'll probably merge since his weapons seems very strong, but I can't decide on the IV.
I have +atk -res and +def -hp, both are very good IVs, untill now I just used him as AA red physical tank, but with his new weapon I can give him either Steady breath or Warding Breath combined with Aegis/Pavise+Shield pulse to keep his weapon effect all the time.
Both +atk and +def seem nice, but I think that -hp is a bit worse than -res as he can easily offset the bane with Aegis.
But I'm not too sure about using Aegis as mages are so rare that I may encounter so many matches in which Aegis results in being useless, which may make Pavise a bit better also because dragons are so common
I'd say +Atk -Res as attack is a better boon and -Res is fine if you're running Shield Pulse. I just built my +Spd -Res Saber and so far he seems really powerful and also still tanky vs mages. I think mages are still pretty common unless you plan on using him in high tier arena, but as an AA check and for PvE content I think +Atk -Res is better.
Here's my Saber build. Without a Breath A Slot, idk how good he'd be.
Pokemon GO
Fire Emblem Heroes
Fate Grand Order
Dragonball Legends
Dragalia Lost
IV Calc
Heroes