When has the decision been made? When the dictator says "make it so" or when the software developers understand the rationale and are able to implement it successfully?

Because the time to the latter is sometimes infinite in the dictatorships I've been in.

(In contrast, when a decision is made democratically, most people are already on board with the implementation details and rationale.)

If you can’t effectively communicate the rationale and intention behind your decisions, you’re failing as a leader. A dictatorship doesn’t work without a competent dictator, just as a democracy doesn’t work without a competent demos.

Yes, especially with big groups. In smaller groups, decision making is usually faster and done by people with more local context in bottoms up organizations. See Team of Teams as a decent reference.