MNK involves a lot of strafing from the rear of the target to the flank.

DRG on the other hand only has one skill that needs to be used from the flank and one from the rear.

Also, in general in order to level you'll be doing instances mainly, so most of the time you'll be able to take advantage of the positions. Even when you can not, DRG has a basic combo that has no positional requirement and MNK has a couple of skills that aren't complete trash even when out of position.

Melee DPS are a bit more involved to play right, but I wouldn't call it punishing since their DPS is far greater than ranged to compensate for this.