My bad for reading your post wrong. But seriously, your point doesn't hold up to the facts.
Against Parker, the opposing point guards average 15.2 points per 48 minutes. That's not only a good mark, it's the best in the NBA for a starting point guard.
Points Against Per 48 Minutes
Parker, Spurs - 15.2
Chalmers, Heat - 15.5
Blake, Blazers - 16.1
Felton, Bobcats - 16.2
Rose, Bulls - 16.8
Davis, Clippers - 16.9
Billups, Nuggets - 17.6
Alston, Rockets - 17.7
Watson, Warriors - 18.3
Ford, Pacers - 18.3
Udrih, Kings - 18.7
Calderon, Raptors - 18.7
Bibby, Hawks - 18.8
Conley, Memphis - 18.9
Miller, 76ers - 19
Rondo, Celtics - 19.1
Harris, Nets - 19.3
Fisher, Lakers - 19.4
Paul, Hornets - 19.8
Nash, Suns - 19.9
Williams, Jazz - 19.9
Kidd, Mavs - 20.6
Nelson, Magic - 20.7
Williams, Cavs - 20.8
Ridnour, Bucks - 21
Foye, T'Wolves - 21
Duhon, Knicks - 21.2
Dixon, Wizards - 21.2
Watson, Thunder - 21.5
Stuckey, Pistons - 26.7
You can call me a Parker homer if you want for pointing out that your assumption is incorrect, however there are the numbers you asked for. Parker is far from a perfect player but to call him out for the player he guards scoring too much doesn't jive with reality when he's in fact the best in the league in the category you say he is weak in.