My take, neither kolb nor Manuel play defense, which has the potential to be a top 3 d. With a stout defense, with a returning stevie, game planning for a run heavy, play action attack, and it doesn't really matter who is in at qb.
With that said, this injury/procedure thing is only news cause it is preseason. IMO, Guys don't randomly have knee procedures without a glaring injury. Manuel will be fine, and this giant thread will be a blip in a month.