Setting one biome throughout the overworld

I am trying to make the biomesoplenty:wasteland be the only biome in the overworld.
I am currently using this script:
{
    "dimensions": {
      "minecraft:overworld": {
        "type": "minecraft:overworld",
        "generator": {
          "type": "minecraft:noise",
          "settings": "minecraft:overworld",
          "biome_source": {
            "type": "minecraft:fixed",
            "biome": "biomesoplenty:wasteland"
          }
        }
      },
      "minecraft:the_nether": {
        "type": "minecraft:the_nether",
        "generator": {
          "type": "minecraft:noise",
          "settings": "minecraft:nether",
          "biome_source": {
            "type": "minecraft:multi_noise",
            "preset": "minecraft:nether"
          }
        }
      },
      "minecraft:the_end": {
        "type": "minecraft:the_end",
        "generator": {
          "type": "minecraft:noise",
          "settings": "minecraft:end",
          "biome_source": {
            "type": "minecraft:the_end"
          }
        }
      }
    }
  }

The problem is that the biome generates, but there is grass and dirt, which should both be replaced by biomesoplenty:dried_salt. Everything else is how it should be...