I wouldnt say so. Lets take a closer look on his support abilities. If you are just talking about Magic Damage output then you have to look up for his and Medienas magic stat.
From 'Skulle' Blackmage Mainjob he can get the support ability "Mag Up lvl 1" and also he can get another one from his rod wielder subjob. So in comparison he can have a 20% higher magic value in comparison.
She stronger than medi (except oppai), look her sub job is compatibel with first job
Wow he can hit a lot of magic points by having two passive magic up. Potentially stronger than the dreaded medienna with both his first and second class, im glad i still dont have any lightning unit, saving for him in global!