I don't feel like this would be really helpful. There's no need to really control disasters when they already happen on its own. Everything has its own order and let's say spawning the wither or letting pvp really early in the game would just be unexpected. Let's say you just spawn and there's already lava falling down when you don't have any armor/tools. Everything has a sequence so it can be fair to everyone. However, if the person can control other things (like adding skeletons, being able to change the spawn rate of chests, giving resistance to all players, venom to all players) than that would be cool since it would add a twist and it would make it harder and more competitive to survive.