MQTTClient should allow user-code to set the QoS level (Adafruit IO MQTT Broker supports QoS of 0 or 1). It currently defaults to a QoS level of 0.

Location: https://github.com/adafruit/Adafruit_IO_Python/blob/master/Adafruit_IO/mqtt_client.py#L191

Docs:
https://www.eclipse.org/paho/clients/python/docs/#id3