I don't care how much "real" power they have. If you actually believe in a meritocracy how can you defend someone getting a job because of their lineage, attending real political events and ceremonies and influencing policies that way? And let's not forget that in many cases, they ACTUALLY have institutional powers they just don't use because they don't have to, the institutions serve their interests all the same.
Sorry for the pointless rant. It just happens way too often.
Not only do most of these monarchs have actual institutional power, but they also typically derieve incredible wealth and income at taxpayer's expense. But liberals love parasites, so this is not too surprising.