Eh, he still has a legendary weapon that has 16 Mt and refining it basically makes it an 18 Mt weapon that also gives +2 Spd/Def/Res which basically gives him 34/34 offenses which looks fine to me.
Like Burgundy and Lil Puddin, I'd go with +Spd since +Atk gives him 37/34 offenses which kind of sandwiches him between Soleil's 38/35 offenses and Legion's 36/35 offenses and Soleil's probably always going to hit harder and faster. +Spd gives him 34/37 offenses and makes him Ayra (33/37) without her sword or Regnal Astra and Lucina (34/36). +Atk would work well if you're intending to mainly use the speed refine option since he'd have 37/39 offenses which would be better than going for the Mt refine for 36/37 offenses if he's +Spd and debatable with speed refine since he'd have 34/42 offenses or go with a Distant Counter, Vantage build on him to ensure he can hit as hard as possible on counter, but Marth might have a better argument for that since he has better sustain with refined Falchion for 3 less attack and bulk in general.
I love and hate how M!Corrin's in this weird spot where if he's =Atk and =Def with refined Yato, they both do the same damage without buffs since 50 total attack equals 15 damage from DA and 30 defense equals 15 damage from Bonfire. Bonfire and especially Ignis scale better, but if you're using any attack boosting and not defense boosting passive like you're doing, DA and DF probably win out.
Y'know, if Wrath were more common, M!Corrin could probably use it well. If anything, that Wo Dao+ with Glimmer/Moonbow you have on him would be much more deadlier and stupider. Berserk Armads, Bonfire, Wrath, and Quickened Pulse on Hector is so dumb.
Did you ever use Moonbow with Wo Dao instead? I'd need to check the calculations, but it's supposed to be stronger or at least more consistent in general. If you're mainly having M!Corrin go after greens and colorless and reds, however, Glimmer might win out since it boosts the damage he's doing, especially if he has WTA. Glimmer's just crappy if the user has WTD since it factors in the actual damage being dealt which isn't that great for physical damage units having to go through the usually higher defense.
The only weird thing about M!Corrin or, well, Corrin and Kana now is that unless it was a mistake on the Edit Brigade help screens, Omega Yato seems to be in existence and refined Yato doesn't have the orange glow. Probably not since refined Yato's effect seems to be a combination of Alpha Yato and Corrin's personal skill while Omega Yato is probably just going to be effective against dragons and have +4 Atk/Spd/Def/Res. RIP Sealed Falchion if that happens since it would trade +1 Atk/Spd/Def/Res for always being active. Stuff is pre-planned, but with how bad the backlash was with the fifth Lyn being our sixth legendary hero and fourth alt to be a legendary hero, Corrin or Kana showing up with Omega Yato would probably rile up even more people even though they would make sense as the next legendary hero of water. There's also the general hate on Awakening and Fates bandwagon in addition to being if they're introduced in a regular banner become a regular alt like paladin Chrom and mage knight Eirika.
Also, apparently the developers fixed the Rauthowl issue where you needed to inherit Fire and Elfire to inherit it. Probably this update or the previous one.
And then there's this thing I saw on the FEH subreddit about making the ultimate Camilla to which I was reminded of Antonykun. WARNING: Kind of lewd with one section of screen tapping.