Well I guess I don't see how a manager can determine if someone is "underperforming relative to what is reasonably expectable" without the issues I mentioned in my first post, namely that there is no objective way to make that determination. Managers will mostly be incentivized to determine that no one is ever underperforming relative to a firing standard.

There is also the more philosophical question of where that standard would come from in the first place. And what if the business finds that the average applicant meets a much higher standard than the current firing standard of the company? It would seem to then make sense to raise the company's own firing standard.