>>64479913
Again, the way that the MP38 and MP40 function isn't strongly different from the old MP18 and MP20 from decades prior, it's the same kind of thinking, only they wanted a folding stock and cheaper manufacture, and the MP38/MP40's design achieves that. If you look at interwar subguns, they are mostly derived from the MP18's school of thought, just with stick mags instead of Luger snail drums.

It's really after WW2 when serious development starts happening in any real capacity to make for more compact and efficient designs, like the Uzi and MP5.

>>64479948
If you want to do it good, you will want either a delayed action or a telescoping bolt.

>>64479951
Your points are all correct.

>Other is a semi-auto pistol by default
Sorta. The Intratec Tec-9 was previously the Interdynamics KG-9 and KG-99 pistols, which were the semi-auto pistol version of their MP9 design, which you can see pictured here: >>64480686

It was proposed to the Swedish army, but they did not think it was necessary, and it was mostly worse than their old m/45 Charlies, not just for the reasons you describe, but also because of durability concerns. So, they turn it into a semi-auto pistol for the U.S market and the rest is history. One of the early gigs of George Kellgren of Kel-Tec fame.