I have noticed Rafa hasn't been dominating the 9+ rallies this year, and great defenders usually dominate those long rallies.
And I guess the more Rafa comes to the net the less defensive he is so the lower his defensive rating will be.
Defense isn't just about getting balls back, its about refusing to come forward.
Rafa comes forward plenty now.
ATP Media have introduced an innovative new ratings system for the Nitto ATP Finals – but what’s the logic behind the numbers? The ‘Skill Set Index’ is a brand new concept in which a tennis player’s attributes are split into four categories – each of which contribute to an overall ‘Skill Set...
Defense is based on the following: Defence
• Forced errors per match
• % shots hit on the run
• Average shot depth on the run
• % returns made
• % returns hit with slice
"% shots hit on the run" would not favor Rafa, because when he's running hard at the ball he actually stops just before he hits the ball, so he's not "on the run" when he makes contact (except for the extremely wide balls like the 'around the net post' shot).
"Average shot depth on the run" won't favor Rafa, because Rafa uses the crosscourt forehand to push the opponent out-wide and its often a short ball to corner of the service box.
And "% returns hit with slice" also won't favor Rafa, because most of his slice is used during the rallies, not on the actual return shot.
All 3 of these things happened in 2005-2010 too, so even during his athletic peak he'd not be considered a great defender, based on this system of grading.