COMLEX
There are times when people do overcome the odds, but if you look at the data of students taking the USMLE at DO schools, they tend to average lower than most MD schools out there. Mind you that a good percentage don't even take the USMLE due to fear of failing. My experience is that the majority of people that scored in the 80th percentile that enters them into the "high tier" category are generally people that turned down MD seats or that the verbal section killed their scores.
If your argument is that exceptions exist, that's a very shallow argument. I don't know of anyone that doesn't believe exceptions exist. I do know of hundreds of premeds that think as soon as they walk into DO school they'll get a 290 and then have reality face them. When people discuss things, they speak of generalities, and if you get into medical school, you better be comfortable with generalities or you'll think every case coming through your door is a rare zebra.