I tend to think Bagration was even a foregone conclusion, I mean look at the aircraft deployments by then. A few hundred Luftwaffe types like the Fw-190A, Me-109G and Ju-88 against thousands of Soviet Yak-9's, La-5's, IL-2's and Pe-2's. The Soviets were also playing around with all their new found industrial might too, with a multitude of specialised variants from long range escort Yaks to specialised anti-tank Yaks with 37-45mm main weapons. The La-5F was at least as good as the Focke Wulf in all respects. And recruitment of liberated forces increasingly resulted in Slovakian Lavochkin squadrons, Polish Yaks and so on.

I think the last time the Eastern Front was within reasonable doubt was immediately prior to Kursk, when Manstein submitted his proposal for a brilliant counterattack at the Donets, but required a retreat to draw in the enemy. Hitler would not release his SS heavy Panzer divisions however, claiming too much valuable (yet unserviceable) equipment would fall into Soviet hands (a ridiculous thing to say at this point).

The Army was committed to Kursk by Hitler but morale was so low he was forced to make promises to individual field commanders (published in a release given by Hitler outlining the operation), that they were to be equipped with the same equipment as the Waffen-SS instead of the same old Panzer IV and StuG (he knew the Panzer IV line was actually being switched to a new StuG, the Jagdpanzer anyway, so all the surplus would be modified as a new variant, whilst Panthers gradually replaced the Pz.IV...plus some new armoured car and tractor types were replacing older ones). The Wehrmacht would begin to look something like the shiny new SS instead of running around with horses and digigng trenches like somebody turned the clock back about thirty years.

In this sense, and its overall impact along the entire Front, I would have to say Kursk was the definitive battle. It should've been avoided like the plague, and Manstein's idea run with. That could've secured the initiative that had been won so determinedly at Kharkov, by I might add the willingness of the Waffen-SS field commanders to disobey Hitler's direct instructions. Instead they deferred to Manstein who won them the battle, and then Hitler decorated them as national heroes. I dare say had they been Wehrmacht officers a permanent stay at Dachau would have been a more likely conclusion.