JD is ranked 196 in the world while Weir is UNRANKED.
As a fellow lefty, I am a fan of Mike Weir's, but he has gotten in to 28 events the past two seasons and only made 2 cuts earning 23 K. His game has not fully recovered from his elbow injury, but he has been given his chances to show that it has.
JD, on the other hand, has made 10 of 14 this year earning almost 700 K the past two season...with 4 more events than Weir, he has made 14 more cuts and about 30x as much $ than Weir. Weir might be a nicer guy than John, but he is not playing anywhere near the level that JD has the past two years.
OK so JD has not had status on the tour since 2006. In that time he has got sponsor exemptions to play in 79 events between 2007 and 2011 in which he made the cut 27 times and more importantly Withdrew 12 times. So basically you give him a special invite for 5 years and there is a 1 in 7 chance that he is going to snub the tournament that gave it to him by walking off half way through the week. John has with the exception of his early couple of years and 2004 and 2005 never lived on the tour with his game. Nobody (with the possible exception of David Duval) has been given more opportunities in the game to shoe that he has it.
Mike just lost his tour card last year so given your arguement above that should give him 4 more years of lackluster performance to turn it around like Johnny did this year and show that he still has it by sqweaking into the top 200 so it justifies giving this guy yet another shot.
