I have a quote I use on FFXI forums from Karinya of Carbuncle server:

WHM are overspecialized in defense. Like PLD, they do better in a place where mobs actually fight back.

When The Treasures of Aht Urghan started getting heavily utilized, the fortunes of Paladins and White Mages went down.  Aht Urghan areas (land of Utsusemispam) changed XP/Merit parties by introducing areas where dedicated tanks and healers are more of a detriment than an asset.   In these areas, the wimpy monsters are killed faster and do less damage than their counterparts outside of ToAU zones; so the likes of Summoners, Red Mages, Scholars, and even Corsairs and Bards subbing White Mage are able to handle all the healing duties as well as their own traditional role.

This, in and of itself, isn’t a bad thing.  Both Paladins and White Mages can change their play style in order fit into the new dynamic.  The bad side to this is that I’ve seen many a player come to the conclusion that Red Mages, Scholars, and Corsairs/Bards subbing White Mage are the best healers — period.  I’ve seen it expressed in many linkshells (including lolCats).

This is fucking moronic.

When you need to move a medium cardboard box of stuff across town, you don’t need a diesel-electric locomotive.  If you really wanna go overboard, you can use a diesel tractor-trailer.  A car or pick-up will do just fine, and are probably the better tools for the job.  However, if someone wanted to make the argument that a car [or pick-up] is the best cargo transporter, period, they’d be labeled a ‘tard.

White Mages’s are to healers what the locomotive is to cargo transport.

Through job-specific equipment and access to Cure V, Curaga IV, and Regen III, a White Mage is unequivocally the most MP efficient healer in the game, with the best enmity control of any other healing capable job.  That means, in a nutshell, White Mages continue to be the top dog.