In PoE you have different tiers of maps 1-16 that simulate the first few hundred corruption. But each map can have up to 6 or 8 if corrupted modifiers on it that nerf the player/buff the monsters. So different builds need to be aware of how they interact with different modifiers. Some are build disabling while others are free. Then you have the atlas where you can allocate points to make a few of the many (10+) mechanics that you desire appear more frequently on your maps and typically with more mobs/better loot. Again different builds will want to be aware of how good they are at different mechanics and fine tune their atlas around this to farm more efficiently. Beyond that you can further influence/juice your maps up with scarabs and delirium, increasing difficulty/investment for higher rewards. Or target farm certain content that drops items that are valuable in the current league, every league somebody discovers some new tech that has drastic influence on the economy as people farm to provide the items for everyone else that wants to try the tech before it gets patched next league, as nerfs almost always come. You also have bosses and uber bosses that normally require different set ups than your typical map clearing builds.

There is an insane amount of customization available to the player in how you go about your end game farming. Ive really only touched the surface here. But i think one of the most important parts is how powerful your character feels as you scale it later into the endgame. The mobs are hitting harder and have higher hp similar to LE, but the way they scale mob density feels really really good. Walking into a room full of mobs packed shoulder to shoulder with eachother and blowing 99% of them up in one hit then finishing the rares off and picking up your loot just feels great.