Worth sacrificing Sheena for Svalinn's Shield?

Like which units are you scared about for FRobin to give him Svalinns? I hardly see any armor effective weapons in arena except for like Micaiah but you have color advantage there. Also I use Fury for my FRobin but I believe there's more invested builds if you have the resources which I do not.

I'd say wait for another Sheena, she's relatively common so you can get her with better IV's eventually and fodder her off to Grima for Svalinn Shield which is a good budget option. Just keep in mind it only negates his armor weakness, he'll still have his dragon weakness.

Fury isn't a bad option.

no one uses hammer, armorslayer, and heavy spear unless the unit comes with it by default and its a budget build

Not that necessary, as it doesn't reverse Falchion's effect. The only people you're protecting him against are probably Armorsmasher Olivias and Wing Sword Caedas...maybe some Armorcrushers...yeah armor slaying weapons are kinda rare.

Not worth it with the double weakness (dragon and armored). Maybe if Svalinn shield comes out as a seal slap it on, but I wouldn't use SI for it.