Maybe I missed it in the design here, but this pseudo-Kafka Postgres implementation doesn't really handle consumer groups very well. The great thing about Kafka consumer groups is it makes it easy to spread the load over several instances running your service. They'll all connect using the same group, and different partitions will be assigned to the different instances. As you scale up or down, the partition responsibilities will be updated accordingly.

You need some sort of server-side logic to manage that, and the consumer heartbeats, and generation tracking, to make sure that only the "correct" instances can actually commit the new offsets. Distributed systems are hard, and Kafka goes through a lot of trouble to ensure that you don't fail to process a message.