Maybe he was adding hype, Paul, but the Soukyoku was undeniably more powerful thna anything in existence at that time. That thing was sealed with powerful spiritual ropes, so that its power wouldn't manifest itself. It took several kido corps members to undo the seal. And only the shihoin special gadget could destroy it...that means it was special. The fact ichigo stopped a thig that powerful only in shikai is quite strange, i would say. AT that time his reiatsu was captain level, and I just can't see any other captain...maybe with the excaption f yama)...stopping the phoenix just like that.
My bet is this: since Oestdu is the zanpakuto creator, as he claims to be. Then he must have created the soukyoku, since it's similar to soul cutters. If not then t means ouetsu only found a way to communicate with the inner spirit and somebody else awakened the soukyoku. If that's the case, I'm frihtened who might have it been to hide somthing this powerful inside his soul.