As far as roles go I think you could make an argument for having "gate keeper" and "lightning rod" categories. Gate keeper units would be characters that can vary how many units they're blocking and thus can avoid unwinnable fights without withdrawing--you know, stuff like Sailors, Angels, Pegasus Riders and Puppeteers. Lightning rods would be durable units with good MR that relieve tank pressure by eating some ranged magic damage that Defense based tanks don't otherwise mitigate. E.g., several of the valks, dark fighters and princesses plus virtually the entire angel crew. Sophie is a gold standard in both categories, fwiw; she can happily face tank lich bolts while letting the most dangerous melee shit wander by so your ranged dps and tanks can murder them in relative peace.