Playing over a year and half on Faerie server, which is a part of Aether Data Centre .

From the time the roulette system introduced, the 'Adventurer in need' was 9/10 of the time is the Healer Role (with occasional Tank) for both Low level, High level and Guildhests.

This was the usual pattern, Healer had insta-queue for Patch 2.1 dungeons (CoB H. - HM H. - PS). As for Patch 2.2 dungeons (LCoA - Hal H. - BryF H.) more 'Adventerur in need' was Healer dominating but Tank was more visible say a ratio fo 7:3 as Healer/Tank. At that time most players started to multi-role, especially Tanks. I've seen most tanks level up thier CNJ/WHM to Lv.50 due to the SpiritBond issue and that tendency to farm Brayflox Hard.

That was the turning point, the Following Patches 2.3, 2.4, and 2.5 all have Tank role as 'Adventurer in Need' was 99% dominating in Low level, High level, Expert level and Guildhests. With exceptions for Healer in need for Guildhests occasionally, that was when I switched from Healing to Tanking.