The Deutschland class Panzerschiffe were never designed to serve with a fleet. They were, instead, cruisers in the classical sense of independent warships intended to range far and wide across the oceans, pounding the enemy as they went. They were the final result of the German experiment with surface commerce raiders, designed to be strong enough to kill the cruisers and destroyers escorting British merchant ships.
This did not require them to be very fast. They had to be fast enough to outrun enemy battleships, of course, but not fast enough to keep pace with normal cruisers. The pocket battleship's defense lay in hit-and-run tactics and in being able to survive combat with lone enemy cruisers, not in speed.
In practice, this didn't work out very well. The French, British, and Japanese all had ships capable of chasing down a Panzerschiff and of killing it before the first one was launched; and more were built during the war.
So the fact that a pocket battleship will slow down a carrier/cruiser fleet is a feature, not a bug; pocket battleships weren't meant to act as screen for capital ships.