MQTT still requires a network connection to publish to (or receive subscription events from) a MQTT server.. so you still have the exact same problem with Doze preventing that. What are you doing to get around that problem, if not exempting your app from battery 'optimisations' ?

Edit: Would anyone care to explain how I am wrong in addition to downvoting me? If Doze blocks network connections to your app when it is backgrounded, how can it receive MQTT events?