The issue is that it's very rare that a 'benevolent' dictatorship stays benevolent. There are plenty of examples through history where a good leader (either hereditary, elected or promoted through other means) did well for decades, only to see their efforts undone by an idiot or tyrant that came afterwards.

Also doesn't help that the people who most want power are those least deserving of it. See many CEOs, and many politicians in general.

Does Singapore work well so far? Sure, by some definitions of working well. Same with China.

But it definitely feels like they're rolling the dice with their systems of governance, and hoping the next leader is someone that actually cares about the health of society rather than a would be authoritarian ruler.