Yeah the Arguebus is rather useless in MTW. Strange, since in 16th century battles arquebusques were important on both land and sea.

The battle for Malta (1565) was almost entirely fought with gunpowder units you find in MTW (although Jannissaries had arquebusques as well by that time). Yet I find they completely don't have the effect in the game that I read about in the book.

Oh, and handguns were introduced in the late 14th century according to a weapon encyclopedia I have. The Arquebus made its appearence around 1500. But I'll admit I don't know the exact definition of an arquebus.