Let me throw this out there. So the subclass has a OA schtick. That seems fine, I can't think of any other subclasses that really have that.
But then we have this crit element at the end, and I wonder if that's the wrong direction. "Big Crits" are already the purview of rogues, barbs, and paladins.... and champions already get more crits. Maybe crits is simply the wrong way to go.
We already have vital strike, but maybe we upgrade it to "greater vital strike", where you get double your prof bonus to damage or something. Yes that's very plain jane.....but I feel like that is the point of this class.....raw pain, nothing fancy, not complex, just.... MOAR....PAIN!