Several PMs have 'wreaked havoc' on the country in various ways, and the monarchy has done SFA to stop or moderate them. Indeed, it would be concerning for democracy if the monarch had the power to intervene. The monarch is not some disinterested god. He/she is a fallible human whose main concern is for his/her own family.
I am quite sure that if Adolf had landed here and established a government, the monarchy would have been happy to be a puppet above it, as long as its own privileges were protected. I really cannot understand why some people regard the royals as a sort of King Arthur when they are clearly just humans, with human desires for self-preservation.