In other words: $1 in 1945 Japan goes much further in terms of development than $1 in 2000s Afghanistan.
Not necessarily. If you ignore the (in reality rather important) "ongoing war" aspect, investing in more backward region should give you better return on investment, not worse. That's because investment, like anything else, suffers from diminishing returns. In backward regions, there are a lot of low-hanging fruits to pick, and small amount of money can go very long way. That's why all the NGOs are talking about microlending etc: even trivial amounts of capital make a huge difference.
FWIW I'm no expert on Germany post-war, but from a personal POV my father was born in 1944 and grew up in post-war Germany (Mainz) and my Opa worked for the city in post-war building reconstruction (knew the story of every building in the centre of the city by heart and when I visited told me everything he knew). So I've some interest in the topic.
As for the rest of your points, plenty of valid observations for the period of the 50s, 60s, 70s but we are talking 1948. The war had barely ended.
It's ridiculous to compare a country recently ravaged by brutal total war which lost 26 million people, millions of which were civilians -- to a country which lost just 400,000, almost all in the armed forces (and, again, was a destination for immigration both before and after).
> but both germany and japan had great recovery, despite also having lost a lot in the war due to bombings and population deaths.
Japan at least didn't have many cars in 1948. This is a central part of Tokyo in 1946: https://c1.staticflickr.com/9/8453/7975138441_b82cdd4372_b.j...
You won't be caught in a traffic jam for sure.
That's Berlin in 1948: https://4.bp.blogspot.com/-7m4GWloP444/WMF6AVrgs-I/AAAAAAAAD...
but both germany and japan had great recovery, despite also having lost a lot in the war due to bombings and population deaths.
The difference is the economic system - USSR always felt that they're under threat from western powers, and devoted a lot of work in heavy production (which translates to military production), and very little civilian production. And even technological growth was kept militarily separate - e.g., they actually had computing but did not "give" that tech up for civilian use, after expending the R&D on it.
Mean while, the US's defence spending on R&D does spill over into civilian use (often due to profit seeking motives, but still this produces good results). Like the internet, GPS, etc. The thing is that centrally planned economies means those that aren't "central" to the planner's mind will be forgotten. But everyone in the country is important in reality - so those who get forgotten will decline.