Y'know what, thinking about it, I think they're kinda even. Artur has a much better start because of his Con, and his growths are really good too. Lute's Con is absolutely terrible and is a bit of a pain to train, but Mage Knight gives her horse access anyway, and she grows even better than Artur. Slayer is sort of irrelevant between them, because Excalibur is crazy good.
@Xenomata "Well my teammate can take care of units that this one can't!" isn't a defense for a unit. A unit that does more with the same build and same required team slots is the better one.