Need Understanding for device management from IoT hub and EventGrid with MQTT broker

Question

I'm developing a solution for managing around 150,000+ life science devices using Azure Cloud. The solution includes tasks like firmware updates, sending commands, retrieving data, and other device operations. I've explored both Azure IoT Hub and Event Grid with an MQTT broker. While both appear capable of handling this scale, Microsoft's documentation notes that IoT Hub only supports MQTT v3 and won't be updated to support newer versions. In contrast, Event Grid supports MQTT v5.

Given the need for a highly secure, scalable, and future-proof architecture—especially since these are life science devices—could you advise which option would be more suitable in the long term?