You think in the US the state controls the billionaires?
I think It's a mutually beneficial relationship. The state can hurt the billionaires, and they can hurt the state. Both of these come at a cost to oneself, so they prefer cooperating for their class interest. Like Chinese billionaires do with their party partners. It's only the ones who cause too much of a ruckus due to greed that get cut down. The others are coddled, like every other capitalist project.
Also I'm pretty sure Cuba is still socialist even though billionaires exist outside of Cub[...]Does that make Cuba no longer socialist?
Yes.