Do you have evidence to support the assertion that it isn't purely percentage based? Perhaps there is some account out there that has the same ratio of prohibited items as knife-depot, but has not been banned?
Whether AdWords should allow "assisted open knife" ads is beside the point. Correct or not, AdWords is counting those as prohibited, the allegation of the OP is that AdWords banning criteria are applied differently to large accounts. I'm suggesting that the criteria is applied _exactly the same_, based on a percentage.
What I'm describing is also how Google Product Listing Ads get moderated: if X% of your items are in violation, your account is automatically shut down, pending appeal. Google sends a warning when you reach (X - Y)%, and another email when you reach X% and your account is shut down. I administrate 30,000+ PLA accounts and deal with this on a daily basis. This banning process is completely automated.