It's a matter of perception.
To us, and to you, a 5.5 hits with weight and pace, spin and placement.
To Nadal, they are pansies who push the ball all the time.
Get better, and you won't see as many "heavy" balls.
For all of us, even little guys like Kolhsreiber hit heavy shots, much less a Tsonga//DelPo/Berdych...