Could you specify the exact SCADA / historian product (and version) you’re using?

Different vendors expose different protocols—OPC UA, MQTT, proprietary SQL APIs, etc.—and several of them already ship with Azure connectors or can publish straight to IoT Hub/Event Hubs without a separate broker.

For most OT applications just MQTT or OPC UA Publisher is good enough. Why do you need the throughput of Kafka in your application?