Can you imagine a 6 foot one or two inch Ferru? To get to #3 in the world at his height in this day and age is incredible. Rosewall was smaller, but that was a different age where the smaller quicker guys had an advantage.
Respectfully,
masterclass
he does it with his fitness and with his fight. he tries to bring the fight.
he also tries to play smart tennis given his limited leverage. for instance he has learned to take the ball early.
he does not give up the court. he tries to play close to the baseline and manages to control the center of the court as much as possible.
finally he plays and practices constantly to keep his ground game tuned up.
I would have to agree general: at 6 foot 1 he would have enjoyed the easy power and perhaps a significantly bigger serve.