There are surely some similarities between the two systems, fair enough. And still you need to differentiate between them so that you don't spread FUD, the most dangerous kind of information in times of Trumpism everywhere.
A dictatorship is characterized as a one-man political system. The best successor is believed to be the choice of that dictator.
In a monarchy on the other hand, all power is in the hands of a family. The best successor is believed to be the descendant of a monarch.
Here's a non-Wikipedia source for you. And another one. And another one.
Then you need to tell the "classical" hereditary monarchy, the ones depicted in history books and probably Game of Thrones or something, apart from a constitutional one. This one is a literal game changer, let me tell you, because in a constitutional monarchy a king/queen does only hold ceremonial power at best, which disqualifies the stated EU monarches as dictatorial, seeing as their political system is effectively a collection of mechanics from democracies, like a party system and the separation of powers (example Netherlands: parties like PvdA (social democrats) and 50PLUS (conservatives/senior focus) debating in the Tweede Kamer (= House of Representatives) about laws and regulations = the legislative, even though King Willem-Alexander is in fact king).
The closest thing to what you describe would be the absolute monarchy which is where I would agree with you that it can be strikingly similar. But we don't have those in the EU (save for Vatican City, maybe), and this is an objective fact. How you feel about this is unimportant.
Now, let's stop the off-topic. Should anyone want to discuss this further with me and others, post to the Off-Topic forum or write me a message.
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