True, DIN certainly is a compromise. Of course the version we're accustomed to is never the 1931 standard committee's original take, but a digital modernization.
The de rigueur digital version is FF DIN by FontFont, which was released in 1995:
https://www.fontshop.com/families/ff-din
The changes made in this 1995 version are described thus:
"The shape of the new FF DIN differs from the original mostly by thinner horizontal strokes and by more fluent curves."
So, sounds like you're absolutely right -- line thickness and curvature were reworked to make the typeface more generally useful. (To my taste, all the weights of FF DIN look excellent on a high-dpi screen.)
I can't give you chapter and verse on this, but when the first autobahns were built, they were composed of straight sections and constant curvature bends. This was perceived by engineers to be the rational way. Landscape designers (who were also involved) eventually convinced the engineers to adopt more sinuous curves, which of course also create transitions (clothoid or Cornu spiral sections) which made the roads easier to drive on.
Found a reference: Driving Germany: The Landscape of the German Autobahn. p.130 onwards.
https://books.google.nl/books?id=Kq_Ys4BlA6cC&lpg=PP1&hl=nl&... (starts on p. 129 really)
I'm not wholly sure about that; the strict adherence to line thickness and limited set of curvature angles make me feel like it was adapted from the "font" created by necessity when using road-painting equipment to write asphalt road signs. It which lends the font a "we couldn't do better in one case so let's at least unify on something" feeling that's slightly modernist, similar to logos from the 70s that use unnecessary all-caps to look "digital" because they work with green-screens that don't display lower-case.