It looks like we are in agreement about rough requirements, but estimate consequences differently. That's precisely what I was talking about - even for China powerhouse it would require 30% of GDP (example number, but it's good enough). My point was that 30% of GDP is an incredibly, astonishingly expensive amount of money to be diverged to a completely new activity.
Just to illustrate - NATO countries are currently haggling about spending even 3% on a military out of all things, and military spending is famously popular in most of the countries among people of power, due to all the corruption and jobs and factories and manufacturing and prestige etc. Poland ramping up spending to 4-5% is seen as extremely overspending (it's rational for survival reasons, but economy may not bear that long term). 30% spending on a thing not benefiting rich class in short to mid term is anathema. Not even grandpa Xi with his totalitarian power would manage that.
Also let's not forget that grandpa Xi has this tiny little victorious invasion of the independent Taiwan planned, likely done in a double push together with his puppet Kim against Korea, and simultaneously conducting a total blockade of the South China Sea for a many years. China may even manage that, but that won't be profitable in the slightest, and during the war all that economy engine will stall due to disrupted shipping and sanctions. They just won't have those 30% of GDP to spend on a side.