Sampras is probably mental toughness player ever, or atlest top3..
So replace with him.
with that terrible serve is easy has mental toughness
all the greats have good things and bad things:
sampras and Mcenroe were bads in clay, because they had one-dimensional game for fast courts.
borg never won slams in hc.
in the case of federer, his mental toughness is maybe the only weakness, he has a good mental toughness but not at the same level of sampras,borg or nadal.
but the perfect player don`t exist.
federer has the perfect game but not the perfect mentality