Exactly: Black Mages were at the top, along with Ranger. Everyone was leveling Black Mage and Ranger. If you weren't a Black Mage or Ranger, the scrublets didn't want you. The real Linkshells still realized the power of other jobs, but a properly geared Black Mage or Ranger would still do the most damage. This idea trickled down to XP parties and everyone thought they needed a Black Mage in the party. That was never the case, nor was it the best way to XP, but people thought it was. I'm glad we moved away from that. I cringed everytime I heard a BLM say "let's set up the Freeze MB" because of the BNS. I stopped inviting Black Mages and I loved it.
See, players started using their heads. I was Meleex3, DRK, BRD, RDM at Main D.Weaps long before ToAU came out. Right now, I can build a level 50 party and go to a non-ToAU area and get better XP without a Black Mage (assuming I invite good players). That's the way it's always been, in XP. People just thought they needed a Black Mage for their womg AncientMagiclol damage.
In ToAU areas, though...Black Mages did get screwed. Partially by the playerbase, partially by SE. Imps and Colibri, while squishy, are terrible targets for a Black Mage. Black Mages can still function in ToAU areas (there are Crawlers, Puks, FlyTraps, and Diremites) but the playerbase has decided that they don't need Black Mages. Will this change? No, I don't think so. Black Mage is extremely useful, but not in the majority of "burn" situations. I have difficulty thinking of a solution SE would implement that would speed BLMs up without slowing XP parties down. Recently, SE seems to be attempting to move their game away from the super-grindfest (when compared with certain other MMOs).
Short version: Yeah, ToAU isn't a friend to the Black Mage.