Dean’s remit was to get promotion and he didn’t, so he failed. Butler’s goal is to gain promotion and if he doesn’t he will have failed. If he fails there will have to be a reevaluation, where there may be a consideration that he could learn and improve next year or he goes.
We are currently 12 games in, so there isn’t a comparison between fans turning on Butler now and those saying Dean should go at the end of the season in May. I don’t think it’s ‘beyond the pale’ to say that the task last year was promotion and Dean failed to achieve that.