The Crimean victory in practice had rather less to do with Manstein and more to do with Hitler deciding to make this the decisive axis of the German advance, while it was Mekhlis's mistake that made the course of the offensive possible. Manstein exploited it brilliantly but it's not to his credit in particular.
And to call Siniavo a Manstein victory is ridiculous. He was supposed to launch an offensive his "victory" meant he was incapable of ever launching. That's only a victory in the sense that Pyrrhus of Epirus was the greatest general of the Pyrrhic war. To be strategically outgeneraled to the extent that Mr. Marty Tzu could not convert this into Northern Light is not a sign of victory unless the sole arbiter is that of statistics, in which case it's less military analysis and more treating war as a mathematics thesis.
The strategic parts of Siniavo had nothing to do with manstein
step 1 hitler orders the 11th army north with the objective of the capturing leningrad
step 2 11th army entrains
step 3 russians launch an enormous offensive against troops in place whilst 11th army is still en route
step 4 11th army arrives into the middle of an already pitched battle without half of their equipment even getting into place yet
step 5 manstein hurls the 11th army into the battle and stop the russians dead in their tracks and inflicts 5 to 1 losses on the attacking russians
step 6 desperate situation in the south calls manstein away and a ton of the 11th army's supporting equipment and airpower so the preposed attack on leningrad is called off
please explain how that is either a pyriac victory or strategic failure on manstein's part?