Luis Diasz doesn't have Mane's physicality as such won't be a direct replacement of Sadio Mane. He could do other things but those sharp runs and tackles that Mane brings to Liverpool attack would be missed as we're already noticing. Mane never gets tired and hardly get injuries. Lets watch to see what Luis Diaz can offer.
I agree with you, Sadio Mane and Luis Diaz are two different types of players, Mane is a player who has great physique, speed and reach whereas Luis Diaz is a player with full skills but not backed by a strong physique. Losing Sadio Mane would be very painful for Liverpool, but Nunez would be a worthy replacement.