http://forum.square-enix.com/ffxiv/t...tch-1.19-Notes

Enemy Type
As the variance in strength between enemies has been reduced (see below), enemy type will not influence EXP yield.
* The exception to the above is those enemies deemed extremely weak or strong.

[dev1027] Enemy attributes have been adjusted.
Certain varieties of enemies who were disproportionately strong for their level have been adjusted in order to make an enemy's level a more accurate indication of it's strength. Based on this revision, enemy characteristics such as strong attack or defense will be kept to within the bounds of level.

The difference in mob strength is basically uniform between all mobs. Only difference is abilities used. If you are lv 40 and a lv 40 mob hits you for 150 dmg, all lv 40 mobs will hit you for 150 dmg. You won;t find one that only hits for 75, or one that hits for 300. Unless it's a NM.