it doesnt disable the mobs spawneggs/spawner... what is good
some Mobs cant be spawned by any way
this includes: Witches, Slimes, Guardian(Elder too), Silverfish,Cavespiders and Blazes
so it need to be fixed that this mobs can spawn with Spawneeggs or Spawner but NOT by natural spawning.
There could also be a config option to disable ALL mobs completly and one that only disables the natural spawning of them.
and when im already on the theme: some things still spawn mobs even if the config option is enabled.. like:
Zombie Village, Dungeons with Zombie,Skeleton,Spider spawner, Shulker in the End and Ultra
i hope this will be in near future update