Even though you are dealing with JSON in both services, there is fundamentally difference between the two.
Azure Event Hubs focuses more on event streaming whereas Azure Service Bus is more focused on high-value enterprise messaging, which denotes Azure service is focused on messages rather than events.
In azure service bus With a topic, every consumer that subscribed to the topic will get each message which means each message is picked up by only 1 consumer. In case of event hub you can have multiple consumers.
You can read from the docs page here