Both were. Stalingrad wasn't alone in what stopped the German advance but it did help guarantee that the Soviet Union wouldn't sue for peace. While the city itself wasn't terribly important, it would have gone a long way in guaranteeing Germany securing the Black Sea, and critical Soviet oil fields. Stalingrad also wasn't exactly a close fight as soon as the Germans bombed out the city, neutralizing the German's chief advantage in motorized vehicles and aircraft and the radios they carried. Comparatively the German army was atrociously equipped and organized for small scale, infantry based close-quarter combat. At the start of the war the German army was able to conduct itself at an organizational and logistical level that no one else could touch; it didn't matter that German tanks were unremarkable and frankly inferior to much of what their neighbors fielded when they could guarantee the right kind of troop presence and firepower anywhere at a scale no one else would match.

Kursk wasn't alone in what ended major offensive operations on the part of Germany in the east, but it was their loudest. The value of it was wildly irrelevant. I think it was Guderian who pleaded with Hitler to not commit the troops to it, stating that no one would have been able to find it on a map, to which Hitler replied he actually agreed that the value of Kursk itself was minor at best.

The value of these two battles rests entirely on where you set the goal posts for success and surrender.

I think that they are both very important in the defeat of Germany. Stalingrad started on July 17, 1942 and ended in February 2, 1943. During this battle the Germans nearly won until the soviets out flanked and destroyed the Romanian and Hungarian forces that were protecting the German 6th army's flanks. This allowed the soviets to surround and starve out the German 6th army causing the complete destruction of that army and forcing surrender. This got rid of one of Germany's strongest infantry divisions and started a slow retreat of the Germans.

Now the battle of Kurst was truly the last German offensive. It started July 5, 1943 and ended on August 23, 1943. now with this offensive it can be noted that the Soviets were warned about the attack before hand due to British intelligence and thus was ready when the Germans arrived. This battle was the first time on the eastern front that the Germans never pushed passed soviet defenses. By the time the German offensive was over there were only 10 operational Panzer V Panthers. this caused German armor on the eastern front to be all but non existent. after this battle the Soviets stopped losing to the Germans and really speed up on the road to Berlin.

So I guess I would say that Stalingrad was the battle that started Germany on the road to defeat and Kursk killed any hope of Germany still coming back and winning in the east and sped up the Soviet advances by knocking out Germany armor capabilities.

Would it not be more accurate to say that Operation Typhoon was the decisive battle of the eastern front?

I mean, after that, there was virtually zero chance of a German victory. The battle of Gazala and army group south's advance into the Caucasus being no more than a dead cat bouncing off the military incompetence of respective British and Russian generals?