Quote Originally Posted by Mhaeric View Post
That poll was during Heavensward during the entirety of which Black Mage did have a significant issue with timer maintenance, and its player population dropped.
The funniest thing is, it's even earlier than Heavensward. Look at the question: What job will be your main in Heavensward? Future tense. Also there are responses as early as June 9, 2015, whereas HW released on the 23 of June that year.

So it can also be extrapolated that people were just hyped for MCH, AST, and DRK at the time too and that's where they swapped to.