Kursk was a strategic defeat, to be sure, but it was a tactical defeat as well. The main reason is that the gathered German mobile force was directed at a salient which had been basically turned into a fortress by the Soviets. Many lines of defense were constructed including a deep line all the way back at the Don - showing the Soviets were not convinced they could stop the Germans in the salient. Much superior results could have been had by choosing a different axis of attack in a different sector, rather than biting off Kursk after it had been fortified. The main reason why is that most casualties were caused via encirclement rather than frontal tank combat versus a staunch defense.
It is only the superior German units and tactics that resulted in the high Russian casualties you describe. The Russians could afford the loss (in purely practical terms), while the Germans could not replace their losses. Then, the Germans had their forces dispersed by the requirement to form a defensive line in Italy after that nation's collapse and armistice.
Richard Overy's "Why the Allies Won" is a good synopsis of the recent scholarship on this, while Chris Bellamy's "Absolute War" is a less readable book overall that covers the same material in more detail. Books from before 1990 (example: Albert Seaton's "The Russo-German War") had very little detail about what actually happened at Kursk from the Soviet side. In regards the mistaken attack on Kursk, Mellenthin's wonderful "Panzer Battles" or Manstein's "Lost Victories" are pretty conclusive on this score.