This is the key. The problem with a dictatorship has never been that they are inherently bad, but because they are extremely unreliable long term. Even a "good" dictator that does almost everything perfectly will only be around for so long, and a bad dictator is very likely around the corner.

The other problem is that at some point the primary goal of the dictator is to remain in power and then their decisions are based on the best options to ensure they stay in power (i.e., suppression of anything that could threaten that), and these decisions are often orthogonal or even opposite to the best options for the country and/or its citizens.