Not sure if you're being factitious, but it sounded like parent's data was already in Kafka.

But you're right, no reason not to start with kinesis in the first place, especially with all the AWS options around it including Kinesis Analytics (Streaming "SQL"), Flink (supported by AWS now) or plain old EMR (Spark, Flink, etc...).

There is a lot of work that goes into maintaining your own Kafka ecosystem, even if you use Confluent, Lenses, etc...

Good question. Kafka is cheaper for things that don't need to go into redshift, and there's a fair amount of engineering effort that would go in to switching those existing systems over.