Yeah, that's what I was meaning by weapon rank.
Also, a new idea, there two types of doll tomes, Combat (Melee and Magic dolls) that are high rank like you said (C+ tomes) and support which are really high rank (B+ tomes). Supports can summon two types of shield dolls. DEF dolls, which when attached to a unit, gives the unit the chance of increased DEF if attacked by melee and arrows and RES dolls, which when attached to a unit, gives the unit the chance of increased RES if attacked by magical attacks. Chance of increase DEF and RES depends on the units SKL while how much it increases depends on the tomes rank. S rank tome summon dolls also has a chance of actually blocking those attacks.
Although, I think this is a bit too far but darn I'm thinking a lot on this...