Are we still trying to justify LoS2's plot? Look, I didn't want to spoil it for all of you, but here's the official epilogue, brought to us by an anonymous leaker:
"And so it was that both Death and Satan were permanently destroyed, putting an end to the ageless suffering of humanity. For from that day on, all would live on in peace and harmony, forever grateful for their blessed existence in a world where no one died, no one was evil, and everyone was a mutant. In the crumbling ashes of Castlevania city, joyful children would come to point and shout in glee at Satan's lifeless and bloodied corpse, and the occasionally fortunate traveler would meet two not-exactly-so-evil vampires, cursed to wander the streets of Castlevania for all eternity. But that traveler would smile, as he'd know, just by looking at them, that everything would be all right -- for Gabriel and Alucard, despite centuries of differences, did love each other after all.
The End."