Maybe we should ask the malfested guys Cass cured or the Fygul Cestemus dude she killed (or any of their averted victims) if they think there's a multiverse? =PI know what you're going to say next, too, that even if all of those things coalesce and the bigger picture future remains the same, the fact that there are differences at all along the path that leads to those events happening, in and of themselves, constitutes a new timeline. And that's where we disagree, as a matter of semantics. They have not as of yet defined the nature of SoulCalibur's timeline, where we could have multiverse or not, what the possibilities really are.
Also, wasn't that literally the plot of "Unbreakable Soul"?
Maybe one of these fellows will weigh in and settle this: