For sure DW is not unknown of in real combat history.
It was used in Japan it was used in Medieval Europe too. Truth is it was not a common practice and was more of an exception than a rule. But it was present.
It really requires a special training to be able to utilize this style, even special weapon combination and is not actually more effective in pure power or offense.
It could give the DW-er an advantage in a surprise attack. In a DW combination 1 of the weapons is actually used for defense and the other for offense.
It's extremely hard and extremely situational that both weapons could be used for a simultaneous attack, if ever.
Excluding the east martial styles, where it has seen some real usage, DW style has seen some occasional usage in Europe too, mainly in the form of a dagger and rapier.
Although historically it is not a common or largely known and used style it has existed.
I don't see a reason to not add it into a game, for sure the reason should not be because historically this style is only exotic and rarely even mentioned.
After all, these are games where you shoot fire and ice from your fingers, i doubt this is more often met historically than DW-ing.
