The rainfall in the mangrove swamp does not match that of the regular swamp.
I honestly don't know which is correct, the mangrove swamp or the regular swamp.
Normal swamp differs from mangrove swamp and normal swamp in Java Edition, but mangrove swamp matches mangrove swamp and normal swamp in Java Edition.
In other words, the downfall of the mangrove swamp and regular swamp biome is the same in Java Edition.

downfall
  **  swamp: 0.5
  mangrove swamp:0.9

However, the mangrove swamp, and the color of the grass block on the regular swamp, has little in-game impact, as it does not affect temperature or downfall.

Steps to Reproduce:
1.Compare the "mangrove_swamp.biome.json" and "swampland.biome.json" downfall in the "definitions/biomes" folder.

Observed Results:
mangrove swamp and swamp downfall values are different

Expected Results:
mangrove swamp and swamp downfall match.