Models which are at best a charicature of some reality as a sole pretense for actions are the problem and distract from the issue of what sorts of controls are appropriate in finance like position limits. Allowing banks to create their own risk models shows whose pockets regulators are in - the Banks pockets. So we talk about Excel and models and don't notice models are distractions that allow banks to do what they please until a trader blows up, when then they can blame the models instead of a lack of controls they don't want in the first place. Get real.