I'll agree that dual wielding is often overdone in most games, but there was more to dual wielding than just using a main gauche. The problem with most dual wielding is that the systems generally get designed such that you're dual wielding a pair of full sized swords instead of the smaller offhand or 2 comparatively small weapons that has almost always happened historically. It's even more problematic when said combat doesn't actually realize that the offhand acts as support to the mainhand rather than acting as another full on weapon that you simply alternate between.
One of the more popular dual wielding fighting styles I've worked with and experienced was using a sword in one hand and an axe in the other. It's an absolutely amazing style for fighting someone with a sword and board since you can use the axe to hook their shield and move them around, which can't be done with a sword. If you do it right, the shield ends up being a bigger risk to them because you're making them fight around it rather than the other way around. The biggest advantage of dual wielding is versatility: you can wield 2 different weapons with different benefits and advantages and, even if you're using two of the same weapon, you can have each of them doing something different and, even more importantly, you can swap on the fly. On the field, southpaws often have a distinct advantage over other people because they're not used to fighting someone with a mirrored stance as opposed to a complimentary one; if you're dual wielding weapons of roughly commensurate size (i.e. not using a rapier and main gauche), you can swap stance on the fly and deny that advantage (or gain it over someone else).
The problem with the implementation of dual wielding in games is that it acts like weapons are only there for attacking, so they only consider the potential offensive advantages, which are basically summed up as "swing more often" because games are forced to simplify. Hell, the major advantages of polearms, even those that *aren't* 10' long, are the fact that you'll have a greater reach than someone using a sword and you also have a 5' long heavy wooden pole to hide behind if they close, neither of which get brought up in most games.
Dual wielding is big in games because, while it's a legitimate combat style in real life, it gets exaggerated benefits in games due to the need to simplify. It doesn't help that you can die without any problems in a game so emphasizing offense over defense is a lot more appealing than it is in real life. Fighting defensively only helps tanks in games; in real life, you either fight defensively or you die because there are no healing potions and there are no respawn points.
Honestly, where ARR is concerned, I doubt we'll see any dual wielding of full sized weapons thanks to the way the devs have set up it up. The only real classes I see dual wielding in ARR are NIN/THF (2 daggers/short swords), *maybe* SAM (katana and wakizashi), and RDM (rapier and main gauche).