I found a OneBlock server called LegionCraft and it is all about building up from your own island and grinding to get stronger.
There are challenging bosses and when you beat them they can drop keys. You can use those keys for rare loot and there are crates with epic gear and rewards.
You can also use chunk hoppers to automate parts of your island. The server says it is not pay to win so it feels more fair if you just want to play and grind.
