I'm looking at some proposed designs made by the Germans, they had an idea for a lowbody assault gun that'd be a replacement for the Marder. They called it the Sturmgeschutz III. Looks interesting too:
Yeah, they only made a single prototype model, shown here in Leipzig's War Museum, but still looks interesting.
The only issue is that it needs the Panzer III chassis (Unlike the Marder, which used Panzer II frames), and they needed them to fight the tanks... even though things like the Char B1s and the Matilda Tank laughed their asses off at the IIIs and could only be blown by AA-guns of all things.
This reinforces that it wasn't the engineers (not fully anyway) that were at fault for the Nazis botching. It shows that administration and quality control was rubbish; see throwing valuable training vehicles into war with their best teachers because idiots. See also making a close air support vehicle that even the Soviets refused to use (helped that the Sturmovik, for all of its flaws, actually could take some beating before going down). Seriously, what imbecile gives a short barrel cannon to what turned out to be a good tank-hunter? Why the fuck did they decide to make said tank hunter the infantry tank and vice versa? Did Hitler himself sit down high on speed and picked what each one would do? It's seeming to me kind of likely.