He isn't too "lightweight" to play a CM role (alongside another CM/DM, in some kind of double pivot) if the circumstances are favourable.
He's clearly nowhere near a complete CM, though. His outstanding qualities are very much on the offensive side of the spectrum. In unfavourable circumstances, he can easily be a liability.
We know this, though - I have a feeling I've made the exact same post at least once before.
He's a very good player - we will hopefully make good use of him for several seasons to come. But he - obviously - has to be used right.