Basically, the game talent is multidimensional, just like a mental talent is mutildinesional either.
For instance, if you'd only watch last two Australian Open of Safin and never saw him play anything else, you would have concluded that the guy is a mental rock..
Apparently , Safin has some aspects of mental talentin which he is extraordinarily strong. And in some aspects he is as brittle as soap bubble..
The thing is .. that opposite to common belief, I do not think that that weakeness hurts Marat really much.. Yes, he bombs from tuneups now and then because of that problem, but the only thing that suffers is his results in those tuneup and therefore his rankings .. But who cares about rankings.. As to the thing that matters, Grand Slams, that is, there were only 2 GS matches to my memory that, I think, costed him.. I.e., you could say he lost them because of a mental fragility in a tournament that he had very good chance of winning otherwise. Lost to Ferrero at RG-2002. Loss to Johansson in the AO final. OK..He could have played better against Sampras in 2001 too.. Perhaps.. In all other GS tournaments, if his game was there, he pretty much delievered, so mental part didn't play much of a role..
Other than that, if you think that someone can win multiple and different GSs without a combination of talent/mentality, you are probably wrong..