To be fair, Obsidian is kinda important. I don't think the Nether is 100% required for beating the game, but it is highly recommended and it's the only place where you can obtain certain blocks and resources, as well as Netherite armor. It's basically power scaling: The less important something is in the grand scheme, to more difficult it is to obtain. Therefore, Obsidian becomes hard as the diamonds you use to mine it.
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