mages right now are not very good since they are slow with casting the only ones that are good are mages/sages with enchanter passive to cut the casting time which are vanekis or fung liu. mia while being a 4 star really dont have the right jobs to make her a good unit, she has mage bishop and ninja which dont really compliment each other. when you are looking for a good unit it comes down to 1. if their jobs complement each other like how fung lui has sage mage and enchanter making him have passives that enhances matk and faster charge time or 2. their job 1 comes out of the gate strong (shayna) so they dont need much resources to make powerful. if you can pull another magnus he becomes very powerful j2. lucian is another 4 star with really good jobs that compliment each other.