Best Divine Dew Investment?

Yeah, that sums it all up pretty well, though I think you could bump Nameless Blade up along side Hauteclere given that their unique refinements make them essentially the same weapon in different shapes.

The shit tier should be separated into meh and shit.

Felicias plate should be on good tier (she doesnt gain THAT much, sometimes u wanna save her specials for melees)

Cymbeline and eschehats shoulf be on meh tier

Winds brand in good

Hinokas in good

Alms falchion in top

I disagree with Cymbeline. It makes Sanaki hit like a tank by just being near a flying unit which is easy to achieve! Def mid tier

Having Zephiel literally not die with Wary Fighter and his Eff+ refine is pretty cool. I mean, he's still probably the worst red armor in the game, but...

reaching 35 res against mages with Fortress Res is pretty fun. Add a seal and you have a 38 def, 40 res tank that doesn't afraid of anything.
(this is the meme build that I'm hoping to get)

I must also object to your Eh tier.
Eckesacks is boring, but it allows Zephiel to tank mages, which is something no other armored sword can do.
Cymbeline and Regal might seem situational, but they are not that hard to pull off. Especially Cymbeline if you combo it with guidance.

On the other hand, I'd place hinoka's spear and wing's brand in the good tier. And the Armads 'upgrade' isn't really that much of an upgrade. Especially seeing how Hector can pull of a dual QR with wary fighter, he can attack twice, and his foe only once.