First, the thread is not really about whether it's a valid way to judge anything, but merely refuting erroneous data.
Second, the data is obviously only good to give a you general idea or what the trend is. You can't really prove anything conclusively with it, no.
Fighters are obviously different, and it also depends on the general talent in the camp, but you can at least infer something about a camps way of approaching a fight and what they teach their fighters. All the fighters share trainers and overall philosophy.
If you wanna be statsy about it, you can't really say anything about fighters skills anyway. The sample size is usually abysmally small in mma, with few fighters having over 20 fights, and even fewer having over 30, and even less shared opponents (also fighters grow and change, so they can be quite different from one year to another, so cross-comparisons are also hard).