I was looking at the dates of when various tanks in WW2 were first designed and produced and noticed that both the Sherman and T34 (both of which incorporate sloped armor) were started (and even completed) before the Germans produced their sloped armor tank, the Pz V Panther. Why was Germany so late in this endeavor? Why do people keep on talking about "superior German technology" if sloped armor didn't start there?
Edit: added second question
Pz III & IV armour wasn't completely unsloped -- it was sloped horizontally. The principle was well known, having been a standard feature of naval vessel design for many decades.
It follows that this was a design trade off, but I'm unaware of the design processes. Nothing comes without cost and heavily sloped armour implies less internal space for crew/ammunition stowage.