Minecraft is an entity system and it seems to work just fine. (Fun fact: Forge Mod Loader makes Minecraft an entity component system.)

having things called entities and components isn't doing ECS. Minecraft is a traditional OOP class hierarchy of entities, which (with Forge) have a Map<String, Object> whose entities are called components.

In the technically superior Fabric ecosystem, you can add fields directly to the entity class using bytecode modification instead of having HashMap overhead on everything. Accessing them is a bit roundabout, but in a way the JIT compiler can optimize.