I far as I understand,there might be multiple joined inheritance entities that are being batched in parallel under different operations.
These entities might be linked to each other or they might not.

Let's say we have two entities types FOO and BAR.
If these two types are not linked, then the statements generated for them can be batched and executed independently.
On the other hand, when these two entities are linked through a relation, the order of execution of the batches is not straight forward. I guess the trigger for executing the batch shall not be only limited to the configured size of the batch, but it shall also take into account the order of the operations made by the user using the API and the relation between the entities.