The Seydlitz was never completed by the Germans. By 1942, the plan was to convert the ship to a carrier, but that work was never completed, either. Work finally stopped in 1943; the ship was scuttled in 1945, and was raised and finally commissioned by the Russians.
The other ship mentioned as “L” would have been the Lützow. She was sold, incomplete, to the Soviets in 1939. She was towed to Russia in 1940, was renamed the Petropavlovsk; sunk by the Germans in 1941, was raised and renamed by the Soviets, survived the war, was renamed again, and later scrapped. She was never completed as a seagoing cruiser.
So except for the submarine program, the rest of the story was much ado about nothing.
As for the 3 completed Hipper class ships, the Admiral Hipper served as a surface raider until damaged; at the end of the war was used to evacuate refugees from the east, was scuttled at her dock at the end of the war and was after the war moved and scrapped.
The Blücher was sunk by a Norwegian shore battery at the beginning of the invasion of that country.
The Prinz Eugen is best known for its raid with the Bismark. She survived the war and two atomic bomb blasts before finally sinking at Kwajalein.
In the end, neither Germans nor Italians had the oil surplus needed to operate big surface fleets. As the war worsen for them, their governments lost the remaining interest in big steel.