Think of all the wars we didn't have :)

Democracies aren't perfect, but they can change, admit mistakes and adapt.

I think it is other way round.

In a democracy ideas are ingrained in public psyche for support. Be it Muslims/Jews/Christians good/bad, immigrants evil, abortion bad all become part of a large percentage of people's belief and changing that requires equally herculean efforts.

In autocracy, people are generally kept aloof of such decisions so you can always switch enemies from Eurasia to Eastasia and no one cares. In case of China, the value of Taiwan/Arunachal/... is mostly egoistical, based on some notion that Qing China boundaries must be restored. If tomorrow a new leadership comes and makes EU kind of setup with Taiwan, people will have no say and most won't care.