It seems to be that custom worldgen seeds for datapacks are not randomized even when the seed is 0, with what I know seed 0 is meant to randomize the seed but I constantly get the same seed without any changes at all.
This issue can be a major inconvenience to people like me wanting to tweak world generation slightly or add new Dimensions/Biomes due to the world always being the same regardless of the world seed due to this issue.