The vast majority of SoV refines have made them rocket up from often mediocrity to excellence. There is a presidence for our expectations, and yet so many characters get shafted even by moderate standards. Marth is a decently good unit, and his weapon allows him to have a combat niche against dragons as well as a buffer. Robin however, is unable to properly counter the one thing his weapon gives him a niche for. Aside from Arena babysitting perhaps, he still needs to be decent unit as an addition to buffing. Both of the units you listed can ve considered solid units with buffing added onto that. The same can not be said for Robin, and his buffs are not strong enough to warrant dragging him around