We are past that now. Now we have advisors, funds, elite accountants, and all kinds of dead easy ways to invest and keep huge wealth long term, for even the most inane person. Plus those people are not accountable to anyone. It's not like a hated heir of a royal who has to tread lightly anymore, lest the senate or the people take them down...
In fact, inane people can even make a great fortune from scratch in this era, what with the various famous-for-being-famous celebrities...
1. Advisors and accountants do not own the wealth - you set the goals. If you want to spend it or mismanage it, they are not going to stop you.
2. The wealthier you are, the more difficult it is to maintain the real value of your wealth, in general.
3. If you have 3 children, they have 3 children and so on, and you split your wealth equally among your children, even a billion turns into only 5 million within 5 generations - and that is if they manage to maintain its real value over time.
And if they do manage it cleverly and get to keep the real value of the wealth? Great! Society is better off, because that means they allocated capital productively within our society, making the economy more efficient.
E.g. maintaining the "real value" is not as much of problem for people having tens of billions (as we increasingly see today). Even if the value drops, they're still multi-billionaires. And diversification strategies today span the globe.
And the "3 children inheritance diffusion" problem is easy to solve: rich people have less kids today than historically.
There's also that:
https://qz.com/694340/the-richest-families-in-florence-in-14...
2. If, on the other hand, there is some survivorship bias going on there and wealth rotates a lot, and some members of wealthy families keep their wealth, that is not as good an outcome but it is still not so bad, as it suggests that as a family's culture degrades their wealth will likely degrade as well.
The opposite. Civilization invented laws so people could pass their wealth and power to their children, to the point that the absolute head of the state was determined by birth and not by skills.
In precivilized tribal cultures there was inheritance of weapons, tools, tents etc. to childrens and of course it played a role beeing born the chieftains son, but no ruler was born that way. They had to directly earn the respect of the tribe, by proving they are good leaders, before they were accepted. Direct democracy, long before the greek "invented" the concept.
I find it strikingly hard to believe that democracy, which is what I assume you’re referring to, is the actual imperative that caused this. If we had managed to avoid WWI it’s really difficult to imagine that we’d still be using a horse drawn buggy and a typewriter.