China has always been ruled by dynasties. I don't see any specific reason why it should change under Xi. It is a wet dream of USA to bring instability to China to weaken rising dragon.
There is only one thing that reliably predicts human behavior: incentives. The incentives of the communist party are much more weakly aligned with the welfare of their people than those in democratic countries. It's as simple as that.
In the past, in order to develop a modern economy, it's been necessary for authoritarian states to relax their grip substantially. China may have found a path forward that allows them to relax substantially less than in the past, and that deeply concerns me, because it may mean that the liberalizing effects of progress are muted in that part of the world - and eventually, maybe the rest.
The exact same thing was true of the West until about 100 years ago.
China's GDP is several times bigger[1] than Vietnam, Korea, India, and Singapore, so spending a smaller percentage is still a larger absolute amount. Even India, the closest competitor that you listed is only 1/5 as big by GDP, and in absolute terms has a smaller military.
[1] https://data.worldbank.org/indicator/NY.GDP.MKTP.CD?order=wb...