Luke the Benchwarmer

Eh, I've never pulled Luke, and the only time I ever see Luke used is during that one Chain Challenge when he's with Roderick(?) and Katarina(?).

While he probably isn't on the same level as Xander (innate DC weapon), Sigurd (anti-mage), Siegbert (speedy + Dark GS), and Chrom, he can definitely hold his own when used with a decent set.

The question is whether you really want to dedicate your time and energy in building up ANOTHER Sword Cavalier when you already have four. Can seem a bit redundant when, but can be useful in Arena Assault.

Personally, I gave mine away to Marisa for Fire Boost before LA!Eliwood came around (but that's mainly because I like Marisa). Luke's a pretty meh unit, he doesn't do anything the four you mentioned don't with his base kit. The higher HP is nice, but even without brave sword neutral Luke has 28 spd, which when paired with his 30/20 defenses doesn't make him a great tank. 34 Atk is good, though, and the 43 Hp isn't nothing, but you're basically limited to a basic brave sword build or some sort of slaying edge/fury thing that aims to make him all-around. Still, like the other guy said, the biggest problem is he's just outclassed by the other sword cavaliers, so unless you love luke for some reason, I think that you won't miss him too much if you kill him off for someone better.

I'd rather keep him than fodder him, Panic Ploy is a seal and Fire Boost is very niche (maybe beside Arden and a few others that could effectively use it). I was in the same boat as you since I use Eldigan and Sigurd much more but Luke is so rare that I'd rather not kill him off.