Henry VIII and Bloody Elizabeth aside, the monarchy definitely lost its legitimacy in the 20th Century, as the Queen did nothing as England legalized abortion and opened England to a barbarian horde (Muslims) that is almost completely in charge.
No monarch who has sat on the throne of any country as it committed suicide should hold her head up.
I gotta agree with you. If a monarch cannot (or will not) intervene when the long-term survival of the nation is at stake, then there is no purpose for having that monarch.