Black Mage is incredibly mobile, especially compared to its history over the years. Sure, you have to plan ahead and know when you need your mobility tools, but in situations of heavy movement, black mage is now even more mobile now than red mage, which was formerly the job considered to be the most mobile caster. And on top of that, black mage still does dramatically more damage than summoner. According to a certain site that compiles data on such things, summoner is providing damage on par with physical ranged while black mage is out damaging almost every other job in the game.