Above observations are true when the conditions you match are simple. I have observed the same several times that when queries are rather simple you are better off with a single node. What happening is that cost of IO dominates.

There is a clear value in making Stream processors work closer to hardware. That does not mean single node can handle does better under all use cases. When the complexity of queries increases and when queries can be portioned, there are use cases where still distributed setup can do better.

I work on WSO2 Stream Processor, https://wso2.com/analytics ( Opensource, Apache Licensed). We have chosen to support both worlds where SP has an HA mode that can two servers in a Hot-warm mode that do 100K event per the second and give you a two-node deployment. If you want more, SP runs on top of Kafka, scales, and support multi-data center deployments as well. If the user is in doubt, he can start small and later switch to Kafka without changing any code.