That's true. There is really no such a component, because any Messaging is designed to get deal just only with single message at a time do not impact other messages.
One channel may accept different messages from different systems, for different business logic, with different atomicity etc...
The EIP catalog doesn't provide something similar, but I think your requirement is like window or buffer from Reactive Streams.
Right, Aggregator can help here. You just need to have some artificial correlationKey (correlation-strategy-expression="1") and provide some batch release strategy.
There is some interest Batcher implementation in the Reactor Spring Extension too.