Things always change... usually for the worse.
But consider that monarchies lasted for hundreds or thousands of years. Democracies all across the West are failing after merely decades, assuming they were ever even successful to begin with.
Well things generally happened slower in preindustrial age. Wars that lasted decades were a norm, now a war that lasts few years some consider long.
It's not like monarchies no longer exist, some do, it's just that they aren't a great example to point at either.
Even assuming that what you wrote is true, the hereditary nature of monarchies also mean that their rulers treat the state as a family, long-term investment.
If you look at rich families, including those worth more than a small country, and the drama they sometimes have, you can realize it can be a good thing, or a very bad thing.
It makes the interpersonal drama of rich and famous into a matter of national security and prosperity.
A monarch may screw over the country through incompetence... but it is nearly impossible to find one that had screwed it over by intent. By contrast, elected officials are fully willing and capable of screwing over their country's and people's entire future just for the sake of winning a single election - after all, that is exactly what the Left are doing with mass immigration.
Then why is North Korea even more fucked up than their Chinese patrons? Even they are a bit annoyed with their local hereditary rule being such a drag, but the fact is that hereditary rulers may be unwilling to take risks in improving the country if only to keep their hold on their position solid too.
And back in the age of monarchies, many rulers didn't even consider it a particularly big deal what language their subjects speak and what customs they practice, so importing settler immigrants was something they considered themselves perfectly right to do.
If the figurehead monarchs of places like Spain, UK, Norway and so on were sadly ignored fountains of great wisdom and leadership advice, you may have had a point, but from my observation they aren't all that different in political views from the norm of generic top socialites of the same region regardless of their backstory.
Sure, you may get useless fops who screw over in a monarchy... but in a democracy, especially elective one, that is all but guaranteed. Qualities one needs to get elected - sociopathy, psychopathy, narcissism, deceitfulness - are the exact opposite of the qualities that leaders of the state should have. So while elected officials may not be useless fops, they will typically be far worse than that.
A successful ruler in a competitive environment, monarch or not, will probably have those traits either way, if not, he will find it hard to be successful despite those lacks. Doesn't that describe people like Machiavelli, Ragnar Lodbrok or Sun Tzu pretty closely?
As the saying goes, it's not a question whether the guy on top will be a bastard, it's whether he will be *our* bastard. The key is to get the ruler(s) to direct such dangerous talents at overt and covert aggression externally, rather than internally.
A toothless dog won't bite you for sure, but it won't make a worthwhile guard dog either.