Question about melee dps

I'm new to the game and have been checking for advice about classes and how to build a proper character. During this quest for knowledge I realized that melee dps classes seem to have an odd catch that I dont see often in MMOs outside of a "rogue" type class, which is positional requirements. I'm not really sure how this works as, up until now, I generally just stood behind bosses/trash in instances just because thats what i'm used to doing from previous games, but here it seems that if I play a monk or dragoon, they have many skills where you have to be on the "flank" or behind the enemy to do decent damage or have an added effect of some sort. Does this mean I have to run back and forth from the back to the side during battles? Also, does this make melee dps the weaker leveling classes since obviously you will never be in position to maximize your damage? It seems rather punishing for fights that involve a lot of movement where ranged can probably just stand back and pew pew.

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.

On the target right around the boss is the inner circle. If you are behind him, then there is only one line between you and the boss (the inner circle). The outside half circle with the pointer telling you which way the boss faces is the start of the "flank" where the line starts on either side of the boss. You can slide a "couple virtual feet" by skirting the target ring where these two meet and get both your flank, and rear attack bonuses.

using a 12 hour clock as a reference:
With the boss facing 12
5-7 = rear
3-5 = flank
7-9 = flank

hope this makes sense.

Yes, melee move back and forth constantly to maximize damage. As for leveling, it depends how you level. If you level through quests, it doesn't matter because nothing is tuned so tight that a front-only DPS wouldn't get through them, quite often you also have quest NPCs tanking. For FATEs you'll usually have someone tank also, as it's best to go around in a small group. If you're planning to level through dungeons, it's best if you group up with a tank for the queues since DPS have the longest queue times. That will slow you down beyond no control if you're alone but it doesn't have anything to do with class mechanics. For the fights you'll naturally have someone else as tank.

Melee classes make up the DPS loss of disconnects by doing more damage when they're connected, and during most fights you can stay on the mobs almost full time when you learn how you need to move.