Entities aren’t coupled because they exist as a concept one level higher. Similarly in the GameObject and MonoBehavior model from Unity the GameObject isn’t much more concrete than an ID since it’s really just a container.
The trouble ECS can get into is where you want a set of components to relate to an Entity but don’t want one or more of the Systems that update that set to run. You end up with more complex System definitions that need to exclude Entities based on extra Component criteria. It gets quite messy to work out looking at the Components that make up an Entity what Systems will run on it.
The trouble ECS can get into is where you want a set of components to relate to an Entity but don’t want one or more of the Systems that update that set to run. You end up with more complex System definitions that need to exclude Entities based on extra Component criteria. It gets quite messy to work out looking at the Components that make up an Entity what Systems will run on it.