I need a cavalry tank that isn't red. Does Frederick *have* to be an attacker?

Hi all, long time no post. I'm having a bit of a dilemma here. A while back, I built an absolutely bangin' Galeforce Eliwood (seriously, he just helped me beat Legendary Robin on Infernal, it was awesome), and...outside of specialized all-nuke teams, I never get to use him. He inevitably loses the red spot on my horse teams to Xander/Sigurd/Eldigan, because without one of them, I really don't have any good cavalry tanks, and I've realized it's because tanky non-red horses are...slim pickings. I haven't been fortunate enough to pull Legendary Ephraim, and Gunter and S!Xander are hot garbage (and I don't even have S!Xander anyway), which basically leaves Frederick.

I know everyone always takes one look at Frederick's attack stat and screams "Death Blow Brave Axe build!", but...I'm starting to think that's so 2017? I feel like neither the brave axe nor 35 neutral attack are what they used to be, and Frederick is sitting there at 36 neutral defense (second highest among all horses, literally only Xander is higher, and Xander can't have a boon in it). Is there a reason not to go +def -spd with a slaying axe-QR-Ignis build on Frederick? He'd be limited to physical tanking, obviously, but that's okay, my Eliwood doesn't have 37 resistance for nothing. Is Frederick really *that* great as a player phase unit to give up on his enemy phase potential? Any insights appreciated.