Let’s start from the top. With the US acting as a spoiler, it’s no good to attack their neighbors. Which means the Asian powers can focus on making things besides bombs and bullets. Such as toasters and cell phones. This even benefits China to an extent ; but with them building economic ties overseas they’ll need a force projection capability . Parking a carrier off a coast is a pretty convincing tactic . Thus their naval expansion. China’s ASMs are their anti-Navy strategy.
If we didn’t exist in the region, the area would evolve into an arms race and war pretty fast. If my smartphone is any indication , we don’t need those folks building WMDs.