You do have a valid point... But to me Tsonga seems pretty solid at net. His net game doesn't really break down too often. But yes there are plenty of players who have better volleys than him.
As for other parts of mentality, what are you talking about? I know positive emotion is good, which Anderson lacks. Isner is a good choice btw.
Well, define mentality.
What about concentration, confidence, resistance to pressure, resistance to adversity. Tactical awareness might fall under another category but I'd include this too. Things like this.
"Mentality" and even "mental strength" and the commonly used "mental toughness" (I don't know why people use this word) is all a bit vague.