@crankycoder in 2.2 with appropriate binding mysensors is working pretty well. All variables are presented with mysensors lib 2.2.
I only updated openhab to 2.3 as this release was presented on my debian system. But I didn't get 2.3 working with mysensors mqtt.

Another thing is that sensor and gateway need a minimum distance. I had gateway and sensor on my desktop for testing and had problems. So I put away the gateway 2 meters and problems are gone. Just a try.

@timo I found the fault in my configuration: it was the missing secure=false config flag in the org.eclipse.smarthome.mqttbroker.cfg config file. I have no idea what happens when the flag is missing but without it one doesn't achieve a valid connection.

name=mosquittomys
host=192.168.96.8
port=1883
secure=false  <-- important !

So now I have a working 2.3 installation! Thanks alot for your support.