Tactically, not exactly. Germany did break through in the south of Kursk.
No, they didn't. They never penetrated into the rear area of the defending Soviet armies, never mind the front-level defenses. They were still stuck in the Soviet defensive lines and had not penetrated into their operational depths when the whole thing was called off.
Being that the Leningrad front, as the OP stated, does not lend itself to many more numbers on either side, this scenario leads to only a tiny incremental change in the number of forces in central Russia and Ukraine.
That's an unproven assumption. The Soviets certainly didn't have problems reinforcing that front and building it up either in for their offensive in the winter of '42/'43 - when they broke the encirclement of the city - nor for the offensive in early-'44. The Germans had planned to ship in an additional army in late-'42, before Stalingrad derailed those plans. The claim that neither side could not build up their numbers is thus ahistoric. But even that aside,
In reality, the Germans didn't fight the ussr to a stop OTL, the Russians outran their supply.
Yes, and that was with the Germans doing so with the air and land forces historically allocated to Citadel. Even the OP proposes stripping out at least the former.
So the Germans can pretty much have the same outcome with less losses by avoiding Kursk, perhaps not be on the back foot so bad
We've been over this before. German losses at Citadel were trivial and they easily recovered. The real killer was simply that German infantry divisions still retained their crippling weakness against massed Soviet armour, and so what really mattered in stopping a Soviet attack was how many Panzer divisions there were, and
where they were. Throughout1943, the Soviets repeatedly demonstrated the ability to overrun defending German infantry who lacked armour support.
This problem with the German infantry being too weak also only worsened as the year wore on, because even unsuccessful Soviet attacks often penetrated to their artillery lines and shot them up before any panzers could arrive and then stall them out and repulse them, meaning the Germans invariably lost tons of tube artillery regardless of how successful their defense and counter-attack. Since artillery is where any modern army's infantry derives the bulk of their firepower both on the defense and offense, this was a crippling problem.
Writers like von Manstein blame Kursk for squandering the German advantage but in fact it's pretty clear from the colossal Soviet numerical advantage in tanks that they never had that offensive advantage in the first place. In the defensive battles of 1943, the repeated pattern was that Army Group South was forced to rush its armoured reserves from one hot spot to another, and whenever they contained one Soviet attack, another would develop from another direction and in another location, pushing the Germans back again.
All the Soviets have to do is launch more attacks than the Germans panzer divisions could respond to. The Germans, with too few forces to cover the length of their front, would race their formations one way or another to shore up the line against a Soviet attack, only to be hit unexpectedly by the main blow in a location where they were too weak to stop it, forcing them to scramble, improvise, and ultimately withdraw. Just as happened throughout 1943.
and get a fourth Kharkov or hold Smolensk.
The Germans tried to get a fourth Kharkov. They failed not due to the losses at Citadel - because those were small enough they had recovered by then - but because the Soviet tank formations did not fall apart like had happened at 2nd and 3rd Kharkov, but instead viciously counter-counter-attacked and prevented the Germans from gaining any momentum. This cost the Soviet tank armies most of their strength, but also sapped and exhausted the just-recovered German panzers strength... only for the following armies to roll into them, forcing the subsequent retreat from Kharkov, though they at least managed to stabilize the line again shortly to the south...
Only for the Soviets to then switch
back to Donets, which the Germans were just
barely able to contain a breakthrough. The Soviets then launched another push towards Poltava, and this the Germans again barely contained by rushing the Panzers from Kharkov. Only
there did the Panzer divisions - worn out from the
defensive fighting - reach the limits of their endurance and the Soviets began to breakthrough. By September the Germans realized that only a withdrawal across the Dneiper river could save them, and the entire Army group was forced to fall back.
But this begs the question, what can the armored spear and the top engineers and such do concentrated south of Leningrad instead of North and South of Kursk? Not a rhetorical question.
Well, the assets - especially the engineering ones - will be useful. The issue with this idea is not that the Germans probably wouldn't succeed in a strategic vacuum where they had no enemy counter-actions to worry about. The problem is that even if the Soviets don't choose to amass local superiority, it'll take the Germans long enough to fight through the defenses around Leningrad for the Soviets and WAllies to launch offensives elsewhere even if the Soviets choose, and the Germans will have to call off the offensives in order to divert forces to fight them off. Fighting through competently held, prepared defenses - even if successful - takes a long time.
However, is it possible for Germany to have local superiority in this sector when the USSR eyes the bulge as per OTL?
No. Because the Soviets might glance at the bulge ATL, but they won't keep at it once they look at the intelligence picture. They made a concerted and well thought out effort to determine the intent of the enemy and they had the assets to succeed, so they succeeded.