Battlecruisers after a war that never comes

Why assume that a world without World War I would still complete German battlecruisers and keep building the type?

At least another battlecruiser generation would probably appear because fast battleships were not yet a fully solved technology; only then might they replace the type.

The Queen Elizabeth class shows designers trying to combine speed with battle-line power, but it did not reliably reach the hoped-for 25 knots. Without the First World War, at least one more generation of battlecruisers would probably appear while designers continued trying to make fast battleships work. Once a fast battleship achieves the necessary speed, it can absorb many battlecruiser tasks, but that transition is not yet complete in this scenario. The answer cautions against assuming that later ship categories would arrive on the same timetable after removing the war that accelerated their development.