(EDIT. Found my problem was caused because the min y of -512 was added to the max height of  384 causing the world to only generate between y -512 and -128. User error I apologize for any inconvenience.)

When decreasing a custom world's min y to around -320 or below (for my case I used -512) the world just generates void or incorrectly. With the generation settings or the datapack it generates void but if you combine the generation settings with the datapack it generates just the deepslate.