He reminds me of Coutinho, who also never sold me at Liverpool. If play wasn't going through Coutinho, he was out of the game (both offensively and defensively). Diaz obviously has a much better defensive workrate, but I don't think he offers enough in an attacking sense when play isn't run straight through him, and for a player reliant on getting the ball and being the main man, a goal or assist every game and a half isn't enough.
To be clear, I'm setting high standards - the point I made is that I'm not sold on him replacing Mane, which is something very few players are capable of doing. Diaz is an excellent footballer and I'm very glad we have him, but he's far from the automatic pick that Mane was and I don't think that I necessarily rank him ahead of Jota/Darwin/Gakpo in that role.