Why isn't there a shortage of healers?

[Ghishlain]

Because many people like myself, have every DPS class leveled to 50, and I Q as healer 99% of the time.

This is a good point, without knowing how S-E tabulated the results, it's possible to get a great dividing between people who "main a healer" versus people who "have a healer leveled to 50".

The SCH/SMN dual job is a good case in point because many people may have leveled SMN and just unlocked SCH just because it was an easy unlock.

Hard to make a good analysis of the numbers without actually knowing the process S-E employed to reach these numbers.