But what if the Germans withdrew behind the Dneiper in April 1943, and the Soviets tried to drive them back early in July. Assuming the Germans still had 17 panzer divisions in the East--before some were pulled out after the Sicilian landings--couldn't this larger force, coupled with the difficulty of attacking in several different places when much of the front consists of a river barrier, have given the Germans a fair chance at halting the attacks?
The Soviets would be in position to try and drive them back well before July. More like late-May. As for giving the Germans a fair chance at halting the attacker? Well, depends on you define "halt". The Soviets can establish bridgeheads at a rate of up to 20 per month even with the Germans dug in on the other side so by August there would be as many bridgeheads as there were IOTL at the start of November 1943. The key problem is that the Germans intelligence is vulnerable to deception and operating essentially blind. This means that even if the Germans effectively respond to the first attack, their forces will be out of place to respond to the inevitable second attack in a timely fashion. Even if these attacks don't outright succeed, they'll greatly enlarge bridgeheads, tying down more and more German forces just to hold the line. And the Germans
will run out of reserves before the Soviets run out of offensives, as the Soviets get to save all the losses they took conducting offensives in July-August as well as those taken defending and attacking in July.
In numerical terms, the difference between Army Group South in September 1943 and that of early-July is actually pretty minor: Army Group South actually had more panzer and panzergrenadier divisions in September then they had at the start of Kursk (17 as opposed to 15) and while individually these divisions were weaker, overall they still contained the same number of tanks (1,200).
In short, the Germans may be able to hold onto their defensive line for several months longer before it breaks but this is more then made up for by the fact that the Soviets themselves are even more months ahead of schedule.
But what if the Germans didn't bother to defend the Nogay steppe(?) or Nikopol bridehead(?) and attempted to stop the Soviets in the narrows of the Perekop, with 17th army(?) units already in the Crimea. In other words, if they were fully behind the dneiper, with larger panzer forces, all--or at least most--uncommitted by the time the Soviets try to outflank the whole position from the north, wouldn't they have stood a chance of repelling/halting the Soviets?
The lower bend of the river D'niepr presents any west-bank defender with a interesting catch-22. Trying to hold the swathe of territory between the D'nepr and Melitopol may have left Germans holding a front of 240 kilometers without any defensive barrier, but to fully hold the great bend would have required the Germans to add another 100 kilometers to that. The Germans would have required even more forces to hold the latter compared to the former. So your basically asking the Germans to sacrifice more of their reserves to hold a longer frontline for the sake of holding more defensible terrain.