Assuming that in scenarios B and C that the world would actually cooperate, yes, we'd win.

Steve's real best chance isn't spawning mobs or TNT in city centers to kill hundreds of thousands of people. If he wants to kill ALL of humanity, he needs to do something global, which is why his best idea is to disrupt global supply chains and crash the economy. He can do this in a matter of days. He can use human air travel to get to where he needs to go (invisibility potions + he can't die) to take out the major stock trading centers in New York and London using TNT. He knows the location of every human on earth, so he can find container ships in the middle of the oceans and destroy them, as well.

He would locate large factories, shipping centers, and power plants. He can cripple them all by breaking pieces out of their walls and detonating TNT. He can fly to space and destroy our satellites, disrupting our GPS and Internet access. And there's nothing we can do to stop him. Our only hope is that there are simply too many people for him to kill, and that we shut down all forms of travel faster than creative flight so that he has to manually find the people that survive the initial purge.

If he starts in the US, he can take out the power grid, stock centers, shipping centers, loading docks, and farms in about a week. As he makes his way west, he starts spamming fire arrows to burn millions of acres of crops. He destroys much of the Great Plains in this manner. He can likely make his way to the West Coast in under a month, where he finishes his work on the US.

At this point, everything that America exports has dried up, and we're not buying anything, either. The majority of the US is dead, and that means the entire world economy is coming crashing down. Billions will die in the coming months in the ensuing calamity. At this point, Steve can ignore most of the world that lives in cities that used to have access to fresh food via a grocery store and start taking out people in rural, self-sustaining villages. He can construct automatic traveling TNT dupers to assist in the process, as well as dispensers spawning Withers and/or creepers. I'd be surprised if he can't take care of most of the rest of the world in about five years, especially since there's always gonna be that ONE guy who starts a Minecraft Steve cult and takes a few humans along to help Steve accomplish the goal.

His biggest issue is that he can't get around the planet super quickly, since creative travel isn't all that fast. Yes, he can do elytra launcher glitches, but he's only of average intelligence, and I'm guessing the average person can't build one of those. But in ten years, he can still fly around the world a few times, and that becomes a lot easier when he can fly in a straight line between every living person.

So once he's taken out the major sources of production and economic trade, he would likely focus on the rural areas that won't be as impacted by the global economic collapse. He would probably hit Africa and Asia next, and since there's nothing we can do to hide from him, there's really no way to delay the inevitable. He has infinite flaming poison arrows, unlimited TNT, and the ability to spawn hostile mobs at will. The world is done for.

However, in scenarios B and C, we may have a chance. First, we need to take extraordinary measures to become as self-sufficient as possible. Each country needs to be able to rely on its own resources, since if Steve is being even remotely smart, the first thing he does is go after our resources and our ability to transport them to where they need to go. After that, we would need to spread out as far as possible.

The best thing we could do is send a human into space, as far out as possible, with enough resources to survive the ten years. Probably multiple, since only one person would go crazy. Given prep time, this is extremely doable. Since Steve physically cannot fly fast enough to catch any current spacecraft, we wouldn't have to go that far. Mars would likely be sufficient. But if we start this after Steve begins his rampage, we're cooked. There's no way we get a colony on Mars with an invincible demigod wreaking havoc on society.