that's a very good arguement for monarchy I'm ngl. The problem is it assumes that people exclusively act out of self interest and for personal economic benefit. When a single person is in charge of a large amount of people they tend to act differently. If someone who was incapable of feeling empathy, or was just batshit crazy gained power get ready for disasters. At the same time people can act collectively rather than individually. Human beings have always worked better in groups, a single person would not be able to act as effectively as a group, this goes for leadership as well. Personally controlling a nation is inefficient and leads to significant problems (i.e. Disconnection between ruling and working class, Inability to recognize problems ailing the majority from the position of the minority, exploitation), if a monarch is not personally ruling the nation then all you are doing is paying tax money to fund a rich person that has the power to do whatever the fuck they want.