Yeah, problem is that even a dictator is benevolent, they can't live forever, and there's no way to prevent a malevolent successor from hiding their true color just long enough till the power is transferred. Then you're back to a malevolent dictatorship.

Ironically this is very similar to what happened with Xi. Rumor had it that the party elders picked him over his rival (Bo) because he seemed to be a more moderate guy. Didn't expect the purges and power consolidation that quickly followed, ouch.

I would even go further and argue that a truly benevolent person will never opt to take power this immense for precisely this reason. Yes, you may be able to do a lot of good during your reign, but the amount of power you amassed during it will almost certainly fall to the wrong hands. Not being able to foresee this is enough to disqualify one from being such a benevolent ruler in my book.