I play White Mage before the roulette system was introduced to the game. At that time the 'bonus' for Adventurer in Need was most of the time Tank/Healer, and I always waited the bonus to change to Healer so I can engage into battle.

DPS luck with bonus was mostly in 8-Players duties, and very rare on the light party runs. When Patch 2.2 was released with the new 'Hard Mode' dungeons, something fishy happened, MOST tanks (WAR & PLD), were leveling up CNJ/WHM and actually prefer to run as White Mage. Then the 'Bonus' started to be in favour of the least on the run (ie Tanks), and its up 'till today. It has been months since I saw High Level or Expert Level with a Bonus for Healers.

Hopefully, when 3.0 FFXIV:Heavensward will be released; Healers will be back in-need with all DarkKnight frenzy all about. That is, if there won't be a spree on any new healing class/job.