The Arishok is shown wielding two weapons that any other race is shown to need both hands to wield only one of them. This is shown in cutscenes so isn't an example of gameplay-story segregation. Granted he is an exceptionally strong Qunari but the fact remains we have yet to see a Dwarf, Elf, or Human do the same.
Okay, so.
First and most important: absence of evidence is not evidence of absence.
This is compounded by the second thing: historical greatswords and similar two-handed weapons were
not too heavy for the average person to, like, pick up and use. There are basically no examples of any such weapon heavier than 6 or 7 kilos. That's not a weight issue.
Historically, dual-wielding occurred but was very uncommon for the excellent reason that using two weapons at the same time is very hard to coordinate. It requires an entirely different form of fighting, like the Filipino purpose-developed martial art
eskrima. And even given that, using two weapons at the same time is still quite difficult from an awareness perspective, which is why virtually all examples of dual-wielding focus on shorter weapons that are easier to control. It doesn't really matter how strong you are: fighting with a massive axe in each hand would mostly be quite useless.
That the arishok dual-wields his Arishok Axes, and that those axes are classified as two-handed weapons in
Inquisition, is effectively meaningless from a lore perspective. Like most gameplay, it is out of sync with plausible lore. If it were lore, it would be out of sync with reality. And even if the arishok's axes were meant to be super heavy in the lore, it wouldn't mean anything for the qunari as a whole, because as you say the arishok is depicted as a fairly exceptional being, independent of race.
It doesn't require much effort to believe that the average qunari is taller and stronger than the average human, elf, or dwarf. Qunari men, for instance, are basically always depicted as
Anthony Davis with horns instead of a unibrow. One doesn't need to make bizarre inferences about qunari lore, based on a conjunction of gameplay conventions and historical misunderstanding, in order to say that.