Hard to believe that Bezos or Gates would find it difficult to hire enough mercenaries to defend their position at the top of the social hierarchy.
History certainly seems to suggest that the ruling class virtually always manage to do this. The main way in which the ruling class looses power has been being displaced by other members of the ruling class, which is why dictators are always especially suspicious of their own army and secret service leaders. For example, after the collapse of the Soviet Union, Russia became a fiefdom of 4 oligarchs pretty quickly, and they were displaced by a high-ranking ex-KGB operative (Putin) and his people, i.e. by a gang from another power center.
What historical evidence to the contrary would you put forward?
My point is that the kind of elite we get in a context of peace and security is very different from the kind we get outside of it. Russia is run by a former member of the security forces, and that is often what happens in a time of disorder. How many other former leaders of Russia were drawn from the security forces, and when?
Yeltsin, a civil engineer, followed Gorbachev in 1991 as the first President of Russia. Putin followed Yeltsin in 1999.
All throughout history, any society of sufficient complexity develops strong hierarchies, with a small ruling elite. Throughout history those ruling elites almost never had a problem exerting sufficient oppression on the majority of the population so as to remain rich and powerful. Indeed it has been argues that the ruling elites of yesteryear were substantially more wealthy in comparison with the rest of the population than today's rich. Ruling families tend to last centuries (e.g. the almost 2000 year rule of Europe by a few families like the House of Habsburg which ruled Austria for > 600 years, or ongoing 2.5K years ruling family in Japan, the Shang dynasty ruled in China for 554 years. House of Saud is ruling for nearly 3 centuries. Etc etc.) We remember the French revolution, because it's so rare.
Contrary to what you claim ("expensive institutions"), oppressing a large number of people into submission is cheap, provided the oppressors cooperate tightly and efficiently. (See also the prevalence of slavery in almost all known societies before industrialisation).
It has been argued that by letting the rich get off with some tax evasion, the population buys them off, buys their acceptance of democracy and low-levels of oppression.