- Kafka couldn't cope up if there are hundreds or few thousands topics. High CPU load, longer startup times...

- Even empty Kafka topic consumes 20MB of on-disk storage (that's 20GB for 1000 topics)

- Inevitable coupling of non-partitioned topic to a particular Kafka broker limiting the storage scale

- Tiered storage was not available previously in Kafka (is it now available in open source version?)

- Native Multi Tenant support with Authentication / Authorization support not available in Kafka (essential for customer based thousands of namespaces and topics)