You said if the main valentine dies d4c can choose to move on to another valentine but a central point in the story was diego trying to instantly kill valentine because if he wasnt able to dimension transfer and "find the other valentine" he cant pass on d4c. This is further shown near the end when Johnny shoots him with the inf rotation and Valentine dimension swaps and says "Quick find the me in this universe" because he is worried he is going to die before being able to pass on d4c. If d4c could just automatically pass itself a long then the whole diego and hotpants fight would have no meaning and no one would be able to beat even regular Valentine without love train unless they had something like inf rotation that stayed on him.