You are making an awful lot of assumptions there. There are plenty of real world examples where a single party having control over a process produces significantly better results (and plenty of counterexamples where it doesn't, of course). How do you justify the assumption that preparing the next generation of leadership is one or the other of those?
> ... States are not obligated to allow such access,
Sufficient influence can be used to ensure access until it is no longer necessary. After all the government is little more than the biggest thug in the room at the end of the day.
> Which billionaire has one of those?
Which billionaire has been incentivized to pursue such a goal? It's extremely expensive.
Does the Saudi state count given that it's an absolute monarchy?