The debate is even more fundamental.
If you think that a "career day" for a QB consists of putting up hundreds of yards down 2 or 3 TD in the 4th quarter is valid....then all these "stats" mean alot.
Sure, but McCourty definitely was beaten on plays, ones that he easily defended in 2010. The sideline go or out and up was a play he owned the QB on in 2010, baiting a throw and closing on it. In 2011, he didn't close and was beaten a handful of times.
Now those are certainly important plays, and the end result is a big difference in his overall play. You cant trade 5 picks and 3 breakups for 8 30+ passes and not consider that a big deal.
However, aside from that part of his game, he played very similar to 2010.
If he doesn't correct the deficient area, he is going to have trouble, but I am confident the skill is there, and whatever cropped up last year will be corrected, and he is back to a top 5 corner.
As far as the 'stats', there are a plethora of issues with them.
1) They are gathered by a company that admits to laking football knowledge
2) Even with football knowledge it is often impossible to 'charge' a catch to a player without knowing the defensive call. In fact, in zone coverage most completions are in the seams of the zone.
3) There is no agreed upon method of calculating these stats
4) There is no data base to compare these stats to in order to assess good or bad
5) As you said, prevent defenses would drastically cause these numbers to soar, when the corner is only doing his job and keeping the play in fromt of him.
6) It is also often impossible to judge who blew a coverage, whether the corner was expecting safety help, whether the linebacker did his job in the underneath zone, and whether or not there was a pass rush.
I could go on.