Both Leica Q and Leica SL have Full frame sized 24.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Another difference between these two cameras is that Leica SL's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the Q Typ 116 and SL sensor size comparison.
Leica Q and Leica SL sensors have exactly the same size so none of them has any advantage over other in this area.