But I take and am a bit heartened by your main point - while the best case authoritarian regime can plan and execute more quickly and with greater efficiency than representative government, the worst case authoritarian govt is much much worse than the worst case possible with a functional democracy.
This requires that those in/with the power actually have altruistic, or at least not solely selfish, concerns. How rampant is government/bureaucratic corruption in China?
I elided the population starving part in order to not distract from the possibility of truly selfless governance strategy. It may very well be the case that millions starving is considered "acceptable losses" ("the needs of the billions outweigh the needs of the millions") in executing on that strategy. Which, make no mistake, would be truly tragic and should be undesirable. But that not everyone sees it that way is really what we're fighting against.
"I have a machine that feeds everyone, no one shall go hungry."
"But mah profits!"
"You only need profits so you yourself can eat, but that's now a solved problem"
"But mah profits. How will we know who's winning?"
Millions starving during the Great Leap forward was very much NOT part of the plan, it was the result of some very misguided agricultural practices.
My point is that in the same period, China has gone from "oops we accidentally caused the 2nd largest mass starvation event in history" to "we have the largest high speed rail network and manufacturing base in the world and nobody is even close."
While the US went from "what's a postwar superpower to do? How bout some megaprojects?" To "I'm drowning in entitlements and houses now cost the same as the average lifetime GDP per capita".
Also, China has its own real estate bubble, so it is not immune to those issues. At least in the US people have some recourse at the individual level.