Direction can certainly be part of it. I'll take your assessment at face value that the actors involved were not without talent. But it all depends on what they're working with--Shakespeare, the dialogue of Soulcalibur has never been--and direction / the studio process. But, I mean, honestly it's fine, it's Soulcalibur: it's almost off-key if the acting isn't hammy, the dialogue barely understandable (and kicked up to 11 on the melodrama scale), the plotting short-shrifted and ham-fisted, and the overall direction disjointed.Really, though lol.
Honestly, SC3's voice acting is a mystery to me. A good number of the English VAs in that game were quite talented and did just fine in their other projects, and yet they all did equally terribly. Whoever the director was for the English version really dropped the ball.
Or at least, you know, when it comes in small doses at the end of micro-story arcs with silly little outcomes for the over-the-top main cast. Rather than being stretched out across hours and hours of the same awfulness featuring cookie-cutter bandits and other NPCs in an un-ending parade of tedium and poor voice work: I can't imagine who would think -that- would be good for a Soulcalibur game...