Yeah, the problem in a dictatorship is that of succession.
Anyone can putsch their way to the top, so even a benevolent dictator is forced to divert most resources towards staying in power, by any means necessary (including large scale violence).
If they don't, they'll be replaced by someone else more ruthless.
That's why there are no "good" dictatorships, ever. It's a form of government that lets the most ruthless grab the power.
The advantage with democracy is that it is slow and most of the time end up with fairly sensible results. Decisions are often so complex that it is impossible for one person to actually understand it all. A consortium of advisors could fill that role, but they have to be benevolent and trustworthy too. Their decisions have to be based on something, so the advisors need researchers and people gathering intelligence and statistics. Those people also have to be trustworthy.
All these layers have to be with as benevolent as possible.
In a well functioning democracy, all layers would feel safe. It is really important to be safe from harm when giving bad news, or telling the dictator/advisors that their idea is really dumb, and would be a waste of resources or have a bad effect.
You could argue that a benevolent dictator would welcome bad news, other arguments. However the difference in power would certainly make it scary anyways.
Succession is another issue, and mental decline. Some people become quite mean in old age.
The closest thing I could envision might work is some sort of semi-democratic technocracy. I still think improving democracy is better though
How do you assure the dictator stays good (corruption, dementia, general personality shift)?
What happens if the dictator is no longer good (died, see above, the world has changed and the dictator can not adapt)?
Sure the dictator can assign ministers for topics outside of their skillset and similar and a head physician to determine when a replacement is needed due to health reasons etc, but a dictatorship is always unnacountable. What if the physician coludes with the vice-dictator to declare the dictator unfit? What if the dictator is actually unfit but accuses the physician of colusion? It has no safety checks against its rulers other than revolution and coup.
Democracy has flaws but so does dictatorship and they are not limited to "what if dictator evil"
While Winston Churchill was problematic to say the least, I do find some truth in his old line that "democracy is the worst form of Government, except for all those other forms that have been tried from time to time."
If by "democracy" you mean the broad philosophy of people having a right to decide the law for themselves in some way, then I would argue that it's better than even a "good" dictator. Dictators can be fickle, capricious, manipulative, and more while appearing to be utterly golden individuals outwardly. What happens when culture changes but the dictator doesn't like where it's going and refuses to change his ways? Is he still "good"? And as others have mentioned, how do you quantify "good" anyhow? You're appealing to a moral standard presumably outside the law, so what happens when that standard doesn't match what the people believe?
Power corrupts, and absolute power corrupts absolutely.
I agree that humans are stupid, and even in a perfect democracy would never do what would actually be best for them. But by collectively making decisions we believe are the best, we can get closer to what's best for us than any dictator could.
Maybe in a far future, some advanced benevolent AI that actually knows better and isn't corrupt can govern for us, like a zookeeper or a parent. But till then, democracy is the best we have.
Democracy does seem to cater people just below average. Good monarchs can easily beat that, but then the new problem presents itself very quickly - good monarchs are far and few between.