That’s a very ahistoric perspective. Many of the longest-lived and most successful empires throughput history have been monarchies and dictatorships. The current popularity of broadly democratic regimes is a very recent development in human history.
Even the US was very undemocratic for most of its history (remember when only white male landowners could vote?), and that didn’t stop its ascendancy to world superpower.
That’s less true the deeper you dig into history. Major political change doesn’t always make a big splash into history.
New leadership in a dictatorship often means a quiet realignment at the top. China tends to use the corruption excuse, but look at the upper leadership after such transitions and you find many new faces.
Even the US was very undemocratic for most of its history (remember when only white male landowners could vote?), and that didn’t stop its ascendancy to world superpower.