Nunez is supposed to fill Firmino’s hole when he goes. He’s not mobile or fast enough to be a wide forward for them in their hoof ball to corner quadrant and run as fast as you can to get ball.
Diaz is supposed to be the Mane replacement, and despite people blowing smoke up his arse sycophantically last season, his numbers were nowhere near what Mane’s were and haven’t improved this season.
Diaz looks to me to be an erratic, slightly quicker version of Coutinho. Don’t let him curl the ball from the edge of the area towards the far post and you’ve mostly stifled him.